The rationale for the term Recovered was the Piast Concept that these territories were once part of the traditional Polish homeland. They had been part of, or fiefs of, a Polish state during the medieval Piast dynasty, several different West Slavic tribes inhabited most of the area of present-day Poland from the 6th century. His realm roughly included all of the area of what would later be named the Recovered Territories, except for the Warmian-Masurian part of Old Prussia and eastern Lusatia. Mieszkos son and successor, Duke Bolesław I Chrobry, upon the 1018 Peace of Bautzen expanded the part of the realm. On Bolesławs death in 1138, Poland for almost 200 years was subjected to fragmentation, being ruled by Bolesławs sons and by their successors, who were often in conflict with each other. Władysław I the Elbow-high, crowned king of Poland in 1320, achieved partial reunification, in the course of the 12th to 14th centuries, Germanic, Dutch and Flemish settlers moved into East Central and Eastern Europe in a migration process known as the Ostsiedlung. In Greater Poland and in Eastern Pomerania, German settlers formed a minority, despite the loss of several provinces, medieval lawyers of the Kingdom of Poland created a specific claim to all formerly Polish provinces that were not reunited with the rest of the country in 1320. They built on the theory of the Corona Regni Poloniae, according to which the state, because of that no monarch could effectively renounce Crown claims to any of the territories that were historically and/or ethnically Polish. Those claims were reserved for the state, which in theory still covered all of the territories that were part of, or dependent on, some of the territories reunited with Poland during the 15th and 16th centuries. However all Polish monarchs until the end of the Polish–Lithuanian Commonwealth in 1795 had to promise to do everything possible to reunite the rest of those territories with the Crown, Mieszkos son Bolesław I established a bishopric in the Kołobrzeg area in 1000–1005/07, before the area was lost again. Despite further attempts by Polish dukes to control the Pomeranian tribes. Successful Christian missions ensued in 1124 and 1128, however, by the time of Bolesławs death in 1138, over the following centuries the area was largely Germanized, although a small Slavic or Polish minority remained.7 million inhabitants. After the death of the last Samboride in 1294, the region was ruled by kings of Poland for a short period, after the Teutonic takeover in 1308 the region became part of the monastic state of the Teutonic Knights. A small area in the west of Pomerelia, the Lauenburg and Bütow Land was granted to the rulers of Pomerania, the medieval Lubusz Land on both sides of the Oder River up to the Spree in the west, including Lubusz itself, also formed part of Mieszkos realm. Poland lost Lubusz when the Silesian duke Bolesław II Rogatka sold it to the Ascanian margraves of Brandenburg in 1248, Brandenburg also acquired the castellany of Santok from Duke Przemysł I of Greater Poland and made it the nucleus of their Neumark region. The Bishopric of Lebus remained a suffragan of the Archdiocese of Gniezno until 1424, the present-day Polish Lubusz Voivodeship comprises most of the former Brandenburgian Neumark territory east of the Oder. After World War I, those parts of the former Province of Posen, Piast dukes continued to rule Silesia following the 12th-century fragmentation of Poland. The Silesian Piasts retained power in most of the region until the early 16th century, the first German colonists arrived in the late 12th century, and large-scale German settlement started in the early 13th century during the reign of Henry I
Map (published in 1917 in the United States) showing Poland at the death of Boleslaw III in 1138
Lubusz Land during the Piast period (marked in yellow).