Osmium
Osmium is a chemical element with symbol Os and atomic number 76. It is a hard, bluish-white transition metal in the platinum group, found as a trace element in alloys in platinum ores. Osmium is the densest occurring element, with an experimentally measured density of 22.59 g/cm3. Manufacturers use its alloys with platinum and other platinum-group metals to make fountain pen nib tipping, electrical contacts, in other applications that require extreme durability and hardness; the element's abundance in the Earth's crust is among the rarest. Osmium is the densest stable element. Calculations of density from the X-ray diffraction data may produce the most reliable data for these elements, giving a value of 22.587±0.009 g/cm3 for osmium denser than the 22.562±0.009 g/cm3 of iridium. Osmium is a hard but brittle metal that remains lustrous at high temperatures, it has a low compressibility. Correspondingly, its bulk modulus is high, reported between 395 and 462 GPa, which rivals that of diamond; the hardness of osmium is moderately high at 4 GPa.
Because of its hardness, low vapor pressure, high melting point, solid osmium is difficult to machine, form, or work. Osmium forms compounds with oxidation states ranging from −2 to +8; the most common oxidation states are +2, +3, +4, +8. The +8 oxidation state is notable for being the highest attained by any chemical element aside from iridium's +9 and is encountered only in xenon, ruthenium and iridium; the oxidation states −1 and −2 represented by the two reactive compounds Na2 and Na2 are used in the synthesis of osmium cluster compounds. The most common compound exhibiting the +8 oxidation state is osmium tetroxide; this toxic compound is formed. It is a volatile, water-soluble, pale yellow, crystalline solid with a strong smell. Osmium powder has the characteristic smell of osmium tetroxide. Osmium tetroxide forms. With ammonia, it forms the nitrido-osmates OsO3N−. Osmium tetroxide is a powerful oxidizing agent. By contrast, osmium dioxide is black, non-volatile, much less reactive and toxic.
Only two osmium compounds have major applications: osmium tetroxide for staining tissue in electron microscopy and for the oxidation of alkenes in organic synthesis, the non-volatile osmates for organic oxidation reactions. Osmium pentafluoride is known; the lower oxidation states are stabilized by the larger halogens, so that the trichloride, tribromide and diiodide are known. The oxidation state +1 is known only for osmium iodide, whereas several carbonyl complexes of osmium, such as triosmium dodecacarbonyl, represent oxidation state 0. In general, the lower oxidation states of osmium are stabilized by ligands that are good σ-donors and π-acceptors; the higher oxidation states are stabilized by strong σ- and π-donors, such as O2− and N3−. Despite its broad range of compounds in numerous oxidation states, osmium in bulk form at ordinary temperatures and pressures resists attack by all acids and alkalis, including aqua regia. Osmium has seven occurring isotopes, six of which are stable: 184Os, 187Os, 188Os, 189Os, 190Os, 192Os.
186Os undergoes alpha decay with such a long half-life ×1015 years 140000 times the age of the universe, that for practical purposes it can be considered stable. Alpha decay is predicted for all seven occurring isotopes, but it has been observed only for 186Os due to long half-lives, it is predicted that 184Os and 192Os can undergo double beta decay but this radioactivity has not been observed yet.187Os is the descendant of 187Re and is used extensively in dating terrestrial as well as meteoric rocks. It has been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons; this decay is a reason. However, the most notable application of osmium isotopes in geology has been in conjunction with the abundance of iridium, to characterise the layer of shocked quartz along the Cretaceous–Paleogene boundary that marks the extinction of the non-avian dinosaurs 65 million years ago. Osmium was discovered in 1803 by William Hyde Wollaston in London, England.
The discovery of osmium is intertwined with that of platinum and the other metals of the platinum group. Platinum reached Europe as platina, first encountered in the late 17th century in silver mines around the Chocó Department, in Colombia; the discovery that this metal was not an alloy, but a distinct new element, was published in 1748. Chemists who studied platinum dissolved it in aqua regia to create soluble salts, they always observed a small amount of a insoluble residue. Joseph Louis Proust thought. Victor Collet-Descotils, Antoine François, comte de Fourcroy, Louis Nicolas Vauquelin observed iridium in the black platinum residue in 1803, but did not obtain enough material for further experiments; the two French ch
Henry IV of England
Henry IV known as Henry Bolingbroke, was King of England from 1399 to 1413, asserted the claim of his grandfather, Edward III, to the Kingdom of France. Henry was born at Bolingbroke Castle in Lincolnshire, his father, John of Gaunt, was the fourth son of King Edward III and enjoyed a position of considerable influence during much of the reign of his nephew King Richard II whom Henry deposed. Henry's mother was Blanche of Lancaster, heiress to the great Lancashire estates of her father Henry of Grosmont, 1st Duke of Lancaster. Henry, having succeeded his father as 2nd Duke of Lancaster, when he became king thus founded the Lancaster branch of the Plantagenet English monarchy, he was the first King of England since the Norman Conquest whose mother tongue was English rather than French. One of Henry's elder sisters, Philippa of Lancaster, married King John I of Portugal, the other, Elizabeth of Lancaster, was the mother of John Holland, 2nd Duke of Exeter, his younger half-sister Katherine of Lancaster, the daughter of his father's second wife, Constance of Castile, was queen consort of the King of Castile.
He had four natural half-siblings born of Katherine Swynford his sisters' governess his father's longstanding mistress and third wife. These four illegitimate children were given the surname Beaufort from their birthplace at the Château de Beaufort in Champagne, France. Henry's relationship with his stepmother, Katherine Swynford, was a positive one, but his relationship with the Beauforts varied. In youth he seems to have been close to all of them, but rivalries with Henry and Thomas Beaufort proved problematic after 1406. Ralph Neville, who had married Henry's half-sister Joan Beaufort, remained one of his strongest supporters, so did his eldest half-brother John Beaufort though Henry revoked Richard II's grant to John of a marquessate. Thomas Swynford, a son from Katherine's first marriage to Sir Hugh Swynford, was another loyal companion. Thomas was Constable of Pontefract Castle. Henry's half-sister Joan Beaufort was the grandmother of Edward IV and Richard III. Joan's daughter Cecily married Richard, Duke of York and had several offspring, including Edward IV and Richard III, making Joan the grandmother of two Yorkist kings of England.
Henry experienced a rather more inconsistent relationship with King Richard II. First cousins and childhood playmates, they were admitted together to the Order of the Garter in 1377, but Henry participated in the Lords Appellants' rebellion against the king in 1387. After regaining power, Richard did not punish Henry, although he did execute or exile many of the other rebellious barons. In fact, Richard elevated Henry from Earl of Derby to Duke of Hereford. Henry spent the full year of 1390 supporting the unsuccessful siege of Vilnius by Teutonic Knights with 70 to 80 household knights. During this campaign he bought captured Lithuanian women and children and took them back to Königsberg to be converted. Henry's second expedition to Lithuania in 1392 illustrates the financial benefits to the Order of these guest crusaders, his small army consisted of over 100 men, including longbow archers and six minstrels, at a total cost to the Lancastrian purse of £4,360. Despite the efforts of Henry and his English crusaders, two years of attacks on Vilnius proved fruitless.
In 1392–93 Henry undertook a pilgrimage to Jerusalem, where he made offerings at the Holy Sepulchre and at the Mount of Olives. He vowed to lead a crusade to'free Jerusalem from the infidel,' but he died before this could be accomplished; the relationship between Henry Bolingbroke and the king met with a second crisis. In 1398, a remark by Thomas de Mowbray, 1st Duke of Norfolk regarding Richard II's rule was interpreted as treason by Henry and Henry reported it to the king; the two dukes agreed to undergo a duel of honour at Gosford Green near Caludon Castle, Mowbray's home in Coventry. Yet before the duel could take place, Richard II decided to banish Henry from the kingdom to avoid further bloodshed. Mowbray himself was exiled for life. John of Gaunt died in February 1399. Without explanation, Richard cancelled the legal documents that would have allowed Henry to inherit Gaunt's land automatically. Instead, Henry would be required to ask for the lands from Richard. After some hesitation, Henry met with the exiled Thomas Arundel, former Archbishop of Canterbury, who had lost his position because of his involvement with the Lords Appellant.
Henry and Arundel returned to England. With Arundel as his advisor, Henry began a military campaign, confiscating land from those who opposed him and ordering his soldiers to destroy much of Cheshire. Henry announced that his intention was to reclaim his rights as Duke of Lancaster, though he gained enough power and support to have himself declared King Henry IV, imprison King Richard and bypass Richard's 7-year-old heir-presumptive, Edmund de Mortimer. Henry's coronation, on 13 October 1399 at Westminster Abbey, may have marked the first time since the Norman Conquest when the monarch made an address in English. Henry consulted with Parliament but was sometimes at odds with the members over ecclesiastical matters. On Arundel's advice, Henry obtained from Parliament the enactment of De heretico comburendo in 1401, w
Unit of measurement
A unit of measurement is a definite magnitude of a quantity and adopted by convention or by law, used as a standard for measurement of the same kind of quantity. Any other quantity of that kind can be expressed as a multiple of the unit of measurement. For example, a length is a physical quantity; the metre is a unit of length. When we say 10 metres, we mean 10 times the definite predetermined length called "metre". Measurement is a process of determining how large or small a physical quantity is as compared to a basic reference quantity of the same kind; the definition and practical use of units of measurement have played a crucial role in human endeavour from early ages up to the present. A multitude of systems of units used to be common. Now there is a global standard, the International System of Units, the modern form of the metric system. In trade and measures is a subject of governmental regulation, to ensure fairness and transparency; the International Bureau of Weights and Measures is tasked with ensuring worldwide uniformity of measurements and their traceability to the International System of Units.
Metrology internationally accepted units of measurement. In physics and metrology, units are standards for measurement of physical quantities that need clear definitions to be useful. Reproducibility of experimental results is central to the scientific method. A standard system of units facilitates this. Scientific systems of units are a refinement of the concept of weights and measures developed for commercial purposes. Science and engineering use larger and smaller units of measurement than those used in everyday life; the judicious selection of the units of measurement can aid researchers in problem solving. In the social sciences, there are no standard units of measurement and the theory and practice of measurement is studied in psychometrics and the theory of conjoint measurement. A unit of measurement is a standardised quantity of a physical property, used as a factor to express occurring quantities of that property. Units of measurement were among the earliest tools invented by humans. Primitive societies needed rudimentary measures for many tasks: constructing dwellings of an appropriate size and shape, fashioning clothing, or bartering food or raw materials.
The earliest known uniform systems of measurement seem to have all been created sometime in the 4th and 3rd millennia BC among the ancient peoples of Mesopotamia and the Indus Valley, also Elam in Persia as well. Weights and measures are mentioned in the Bible, it is a commandment to have fair measures. In the Magna Carta of 1215 with the seal of King John, put before him by the Barons of England, King John agreed in Clause 35 "There shall be one measure of wine throughout our whole realm, one measure of ale and one measure of corn—namely, the London quart; as of the 21st Century, multiple unit systems are used all over the world such as the United States Customary System, the British Customary System, the International System. However, the United States is the only industrialized country that has not yet converted to the Metric System; the systematic effort to develop a universally acceptable system of units dates back to 1790 when the French National Assembly charged the French Academy of Sciences to come up such a unit system.
This system was the precursor to the metric system, developed in France but did not take on universal acceptance until 1875 when The Metric Convention Treaty was signed by 17 nations. After this treaty was signed, a General Conference of Weights and Measures was established; the CGPM produced the current SI system, adopted in 1954 at the 10th conference of weights and measures. The United States is a dual-system society which uses both the SI system and the US Customary system; the use of a single unit of measurement for some quantity has obvious drawbacks. For example, it is impractical to use the same unit for the distance between two cities and the length of a needle, thus they would develop independently. One way to make large numbers or small fractions easier to read, is to use unit prefixes. At some point in time though, the need to relate the two units might arise, the need to choose one unit as defining the other or viceversa. For example an inch could be defined in terms of a barleycorn.
A system of measurement is a collection of units of measurement and rules relating them to each other. As science progressed, a need arose to relate the measurement systems of different quantities, like length and weight and volume; the effort of attempting to relate different traditional systems between each other exposed many inconsistencies, brought about the development of new units and systems. Systems of measurement in modern use include the metric system, the imperial system, United States customary units. Many of the systems of measurement, in use were to some extent based on the dimensions of the human body; as a result, units of measure could vary not only from location to location, but from person to person. Metric systems of units have evolved since the adoption of the original metric system in France in 1791; the current international standard metric system is the International System of Units. An important feature of modern systems is standardization; each unit has a universally recognized size.
Both the imperial units and US customary
Denarius
The denarius was the standard Roman silver coin from its introduction in the Second Punic War c. 211 BC to the reign of Gordian III, when it was replaced by the Antoninianus. It continued to be minted in small quantities for ceremonial purposes and through the tetrarchy; the word dēnārius is derived from the Latin dēnī "containing ten", as its value was of 10 assēs. The word for "money" descends from it in Italian, Slovene and Spanish, its name survives in the dinar currency. Its symbol is represented in Unicode as, however it can be represented as X̶. A predecessor of the denarius was first struck in 267 BC, five years before the First Punic War, with an average weight of 6.81 grams, or 1⁄48 of a Roman pound. Contact with the Greeks prompted a need for silver coinage in addition to the bronze currency that the Romans were using at that time; the predecessor of the denarius was a Greek-styled silver coin called the didrachm, struck in Neapolis and other Greek cities in southern Italy. These coins were inscribed for Rome but resemble their Greek counterparts.
They were most used for trade purposes and were used in Rome. The first distinctively Roman silver coin appeared around 226 BC. Classic historians sometimes called these coins denarii, but they are classified by modern numismatists as quadrigati, derived from the quadriga, or four-horse chariot, on the reverse, which with a two-horse chariot or biga was the prototype for the most common designs used on Roman silver coins for the next 150 years. Rome overhauled its coinage around 211 BC and introduced the denarius alongside a short-lived denomination called the victoriatus; this denarius contained 1⁄72 of a Roman pound, of silver. It formed the backbone of Roman currency throughout the Roman republic; the denarius began to undergo slow debasement toward the end of the republican period. Under the rule of Augustus its silver content fell to 3.9 grams. It remained at nearly this weight until the time of Nero, when it was reduced to 1⁄96 of a pound, or 3.4 grams. Debasement of the coin's silver content continued after Nero.
Roman emperors reduced its content to 3 grams around the late 3rd century. The value at its introduction was 10 asses, giving the denarius its name, which translates as "containing ten". In about 141 BC, it was re-tariffed at 16 asses; the denarius continued to be the main coin of the Roman Empire until it was replaced by the antoninianus in the middle of the 3rd century. The coin was last issued, in bronze, under Aurelian between AD 270 and 275, in the first years of the reign of Diocletian.. It is difficult to give rough comparative values for money from before the 20th century, as the range of products and services available for purchase was so different. Classical historians say that in the late Roman Republic and early Roman Empire the daily wage for an unskilled laborer and common soldier was 1 denarius or about US$2.80 in bread. During the republic, legionary pay was 112.5 denarii per year doubled by Julius Caesar to 225 denarii, with soldiers having to pay for their own food and arms.
Centurions received higher pay: under Augustus, the lowest rank of centurion was paid 3,750 denarii per year, the highest rank, 15,000 denarii. The silver content of the denarius under the Roman Empire was about 50 grains, 3.24 grams, or 1⁄10 troy ounce. On June 6, 2011, this was about US$3.62 in value. The fineness of the silver content varied with economic circumstances. From a purity of greater than 90% silver in the 1st century AD, the denarius fell to under 60% purity by the year 200, plummeted to 5% purity by the year 300. By the reign of Gallienus, the antoninianus was a copper coin with a thin silver wash. By comparison, a laborer earning the minimum wage in the United States in January 2014 made US$58 for an 8-hour day, before taxes and an employee earning the minimum wage in the United Kingdom in 2014 made £52 for an 8-hour day, before taxes. In the final years of the 1st century BC Tincomarus, a local ruler in southern Britain, started issuing coins that appear to have been made from melted down denarii.
The coins of Eppillus, issued around Calleva Atrebatum around the same time, appear to have derived design elements from various denarii such as those of Augustus and M. Volteius. After the denarius was no longer issued, it continued to be used as a unit of account, the name was applied to Roman coins in a way, not understood; the Arabs who conquered large parts of the land that once belonged to the Eastern Roman Empire issued their own gold dinar. The lasting legacy of the denarius can be seen in the use of "d" as the abbreviation for the British penny until 1971, it survived in France as the name of a coin, the denier. The denarius survives in the common Arabic name for a currency unit, the dinar used from pre-Islamic times, still used in several modern Arab nations; the major currency unit in former Principality of Serbia, Kingdom of Serbia and former Yugoslavia was dinar, it is still used in present-day Serbia. The Macedonian currency denar is derived from the Roman denarius; the Italian word
Roman currency
Roman currency for most of Roman history consisted of gold, bronze and copper coinage. From its introduction to the Republic, during the third century BC, well into Imperial times, Roman currency saw many changes in form and composition. A persistent feature was the inflationary replacement of coins over the centuries. Notable examples of this followed the reforms of Diocletian; this trend continued into Byzantine times. Because of the economic power and longevity of the Roman state, Roman currency was used throughout western Eurasia and northern Africa from classical times into the Middle Ages, it served as a model for the currencies of the Muslim caliphates and the European states during the Middle Ages and the Modern Era. Roman currency names survive today in many countries; the manufacture of coins in the Roman culture, dating from about the 4th century BC influenced development of coin minting in Europe. The origin of the word "mint" is ascribed to the manufacture of silver coin at Rome in 269 BC at the temple of Juno Moneta.
This goddess became the personification of money, her name was applied both to money and to its place of manufacture. Roman mints were spread across the Empire, were sometimes used for propaganda purposes; the populace learned of a new Roman Emperor when coins appeared with the new Emperor's portrait. Some of the emperors who ruled only for a short time made sure; the Romans cast their larger copper coins in clay moulds carrying distinctive markings, not because they did not know about striking, but because it was not suitable for such large masses of metal. Roman adoption of metallic commodity money was a late development in monetary history. Bullion bars and ingots were used as money in Mesopotamia since the 7th millennium BC. Coinage proper was only introduced by the Roman Republican government c. 300 BC. The greatest city of the Magna Graecia region in southern Italy, several other Italian cities had a long tradition of using coinage by this time and produced them in large quantities during the 4th century BC to pay for their wars against the inland Italian groups encroaching on their territory.
For these reasons, the Romans would have known about coinage systems long before their government introduced them. The reason behind Rome's adoption of coinage was cultural; the Romans had no pressing economic need. However, Roman coinage saw limited use; the type of money introduced by Rome was unlike. It combined a number of uncommon elements. One example is the aes signatum, it measured about 160 by 90 millimetres and weighed around 1,500 to 1,600 grams, being made out of a leaded tin bronze. Although similar metal currency bars had been produced in Italy and northern Etruscan areas, these had been made of Aes grave, an unrefined metal with a high iron content. Along with the aes signatum, the Roman state issued a series of bronze and silver coins that emulated the styles of those produced in Greek cities. Produced using the manner of manufacture utilised in Greek Naples, the designs of these early coins were heavily influenced by Greek designs; the designs on the coinage of the Republican period displayed a "solid conservatism" illustrating mythical scenes or personifications of various gods and goddesses.
In 27 BC, the Roman Republic came to an end. Taking autocratic power, it soon became recognized that there was a link between the emperor's sovereignty and the production of coinage; the imagery on coins took an important step when Julius Caesar issued coins bearing his own portrait. While moneyers had earlier issued coins with portraits of ancestors, Caesar's was the first Roman coinage to feature the portrait of a living individual; the tradition continued following Caesar's assassination, although the imperators from time to time produced coins featuring the traditional deities and personifications found on earlier coins. The image of the Roman emperor took on a special importance in the centuries that followed, because during the empire, the emperor embodied the state and its policies; the names of moneyers continued to appear on the coins until the middle of Augustus' reign. Although the duty of moneyers during the Empire is not known, since the position was not abolished, it is believed that they still had some influence over the imagery of the coins.
The main focus of the imagery during the empire was on the portrait of the emperor. Coins were an important means of disseminating this image throughout the empire. Coins attempted to make the emperor appear god-like through associating the emperor with attributes seen in divinities, or emphasizing the special relationship between the emperor and a particular deity by producing a preponderance of coins depicting that deity. During his campaign against Pompey, Caesar issued a variety of types that featured images of either Venus or Aeneas, attempting to associate himself
Kingdom of Great Britain
The Kingdom of Great Britain called Great Britain, was a sovereign state in western Europe from 1 May 1707 to 31 December 1800. The state came into being following the Treaty of Union in 1706, ratified by the Acts of Union 1707, which united the kingdoms of England and Scotland to form a single kingdom encompassing the whole island of Great Britain and its outlying islands, with the exception of the Isle of Man and the Channel Islands; the unitary state was governed by a single parliament and government, based in Westminster. The former kingdoms had been in personal union since James VI of Scotland became King of England and King of Ireland in 1603 following the death of Elizabeth I, bringing about the "Union of the Crowns". After the accession of George I to the throne of Great Britain in 1714, the kingdom was in a personal union with the Electorate of Hanover; the early years of the unified kingdom were marked by Jacobite risings which ended in defeat for the Stuart cause at Culloden in 1746.
In 1763, victory in the Seven Years' War led to the dominance of the British Empire, to become the foremost global power for over a century and grew to become the largest empire in history. The Kingdom of Great Britain was replaced by the United Kingdom of Great Britain and Ireland on 1 January 1801 with the Acts of Union 1800; the name Britain descends from the Latin name for the island of Great Britain, Britannia or Brittānia, the land of the Britons via the Old French Bretaigne and Middle English Bretayne, Breteyne. The term Great Britain was first used in 1474; the use of the word "Great" before "Britain" originates in the French language, which uses Bretagne for both Britain and Brittany. French therefore distinguishes between the two by calling Britain la Grande Bretagne, a distinction, transferred into English; the Treaty of Union and the subsequent Acts of Union state that England and Scotland were to be "United into One Kingdom by the Name of Great Britain", as such "Great Britain" was the official name of the state, as well as being used in titles such as "Parliament of Great Britain".
Both the Acts and the Treaty describe the country as "One Kingdom" and a "United Kingdom", which has led some much publications into the error of treating the "United Kingdom" as a name before it came into being in 1801. The websites of the Scottish Parliament, the BBC, others, including the Historical Association, refer to the state created on 1 May 1707 as the United Kingdom of Great Britain; the term United Kingdom was sometimes used during the 18th century to describe the state, but was not its name. The kingdoms of England and Scotland, both in existence from the 9th century, were separate states until 1707. However, they had come into a personal union in 1603, when James VI of Scotland became king of England under the name of James I; this Union of the Crowns under the House of Stuart meant that the whole of the island of Great Britain was now ruled by a single monarch, who by virtue of holding the English crown ruled over the Kingdom of Ireland. Each of the three kingdoms maintained laws.
Various smaller islands were in the king's domain, including the Isle of Man and the Channel Islands. This disposition changed when the Acts of Union 1707 came into force, with a single unified Crown of Great Britain and a single unified parliament. Ireland remained formally separate, with its own parliament, until the Acts of Union 1800; the Union of 1707 provided for a Protestant-only succession to the throne in accordance with the English Act of Settlement of 1701. The Act of Settlement required that the heir to the English throne be a descendant of the Electress Sophia of Hanover and not be a Catholic. Legislative power was vested in the Parliament of Great Britain, which replaced both the Parliament of England and the Parliament of Scotland. In practice it was a continuation of the English parliament, sitting at the same location in Westminster, expanded to include representation from Scotland; as with the former Parliament of England and the modern Parliament of the United Kingdom, the Parliament of Great Britain was formally constituted of three elements: the House of Commons, the House of Lords, the Crown.
The right of the English peerage to sit in the House of Lords remained unchanged, while the disproportionately large Scottish peerage was permitted to send only 16 representative peers, elected from amongst their number for the life of each parliament. The members of the former English House of Commons continued as members of the British House of Commons, but as a reflection of the relative tax bases of the two countries the number of Scottish representatives was reduced to 45. Newly created peers in the Peerage of Great Britain were given the automatic right to sit in the Lords. Despite the end of a separate parliament for Scotland, it retained its own laws and system of courts, As its own established Presbyterian Church, control over its own schools; the social structure was hierarchical, the same elite remain in control after 1707. Scotland continued to have its own excellent universities, with the strong intellectual community in Edinburgh, The Scottish Enlightenment had a major impact on British and European thinking.
As a result of Poynings' Law of 1495, the Parliament of Ireland was subordinate to the Parliament of England, after 1707 to the Parliament of Great Britain. The Westminster parliament's Declaratory Act 1719 (also called the Dependency of Ireland
United States
The United States of America known as the United States or America, is a country composed of 50 states, a federal district, five major self-governing territories, various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U. S. is the third most populous country. The capital is Washington, D. C. and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico; the State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean; the U. S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The diverse geography and wildlife of the United States make it one of the world's 17 megadiverse countries.
Paleo-Indians migrated from Siberia to the North American mainland at least 12,000 years ago. European colonization began in the 16th century; the United States emerged from the thirteen British colonies established along the East Coast. Numerous disputes between Great Britain and the colonies following the French and Indian War led to the American Revolution, which began in 1775, the subsequent Declaration of Independence in 1776; the war ended in 1783 with the United States becoming the first country to gain independence from a European power. The current constitution was adopted in 1788, with the first ten amendments, collectively named the Bill of Rights, being ratified in 1791 to guarantee many fundamental civil liberties; the United States embarked on a vigorous expansion across North America throughout the 19th century, acquiring new territories, displacing Native American tribes, admitting new states until it spanned the continent by 1848. During the second half of the 19th century, the Civil War led to the abolition of slavery.
By the end of the century, the United States had extended into the Pacific Ocean, its economy, driven in large part by the Industrial Revolution, began to soar. The Spanish–American War and World War I confirmed the country's status as a global military power; the United States emerged from World War II as a global superpower, the first country to develop nuclear weapons, the only country to use them in warfare, a permanent member of the United Nations Security Council. Sweeping civil rights legislation, notably the Civil Rights Act of 1964, the Voting Rights Act of 1965 and the Fair Housing Act of 1968, outlawed discrimination based on race or color. During the Cold War, the United States and the Soviet Union competed in the Space Race, culminating with the 1969 U. S. Moon landing; the end of the Cold War and the collapse of the Soviet Union in 1991 left the United States as the world's sole superpower. The United States is the world's oldest surviving federation, it is a representative democracy.
The United States is a founding member of the United Nations, World Bank, International Monetary Fund, Organization of American States, other international organizations. The United States is a developed country, with the world's largest economy by nominal GDP and second-largest economy by PPP, accounting for a quarter of global GDP; the U. S. economy is post-industrial, characterized by the dominance of services and knowledge-based activities, although the manufacturing sector remains the second-largest in the world. The United States is the world's largest importer and the second largest exporter of goods, by value. Although its population is only 4.3% of the world total, the U. S. holds 31% of the total wealth in the world, the largest share of global wealth concentrated in a single country. Despite wide income and wealth disparities, the United States continues to rank high in measures of socioeconomic performance, including average wage, human development, per capita GDP, worker productivity.
The United States is the foremost military power in the world, making up a third of global military spending, is a leading political and scientific force internationally. In 1507, the German cartographer Martin Waldseemüller produced a world map on which he named the lands of the Western Hemisphere America in honor of the Italian explorer and cartographer Amerigo Vespucci; the first documentary evidence of the phrase "United States of America" is from a letter dated January 2, 1776, written by Stephen Moylan, Esq. to George Washington's aide-de-camp and Muster-Master General of the Continental Army, Lt. Col. Joseph Reed. Moylan expressed his wish to go "with full and ample powers from the United States of America to Spain" to seek assistance in the revolutionary war effort; the first known publication of the phrase "United States of America" was in an anonymous essay in The Virginia Gazette newspaper in Williamsburg, Virginia, on April 6, 1776. The second draft of the Articles of Confederation, prepared by John Dickinson and completed by June 17, 1776, at the latest, declared "The name of this Confederation shall be the'United States of America'".
The final version of the Articles sent to the states for ratification in late 1777 contains the sentence "The Stile of this Confederacy shall be'The United States of America'". In June 1776, Thomas Jefferson wrote the phrase "UNITED STATES OF AMERICA" in all capitalized letters in the headline of his "original Rough draught" of the Declaration of Independence; this draft of the document did not surface unti
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