The United Kingdom of the Netherlands is the unofficial name given to the Kingdom of the Netherlands as it existed between 1815 and 1830. The United Netherlands was created in the aftermath of the Napoleonic Wars through the fusion of territories that had belonged to the former Dutch Republic, Austrian Netherlands, and Prince-Bishopric of Liège in order to form a buffer state between the major European powers. The polity was a constitutional monarchy, ruled by William I of the House of Orange-Nassau.

Belgium, officially the Kingdom of Belgium, is a country in Northwestern Europe. The country is bordered by the Netherlands to the north, Germany to the east, Luxembourg to the southeast, France to the south, and the North Sea to the west. It covers an area of 30,689 km2 (11,849 sq mi) and has a population of more than 11.5 million, making it the 22nd most densely populated country in the world and the 6th most densely populated country in Europe, with a density of 376/km2 (970/sq mi). Belgium is part of an area known as the Low Countries, historically a somewhat larger region than the Benelux group of states, as it also included parts of northern France. The capital and largest metropolitan region is Brussels; other major cities are Antwerp, Ghent, Charleroi, Liège, Bruges, Namur, and Leuven.