Various Germanic tribes have inhabited the northern parts of modern Germany since classical antiquity. A region named Germania was documented before AD 100. In the 10th century, German territories formed a central part of the Holy Roman Empire. During the 16th century, northern German regions became the centre of the Protestant Reformation. Following the Napoleonic Wars and the dissolution of the Holy Roman Empire in 1806, the German Confederation was formed in 1815. In 1871, Germany became a nation-state when most of the German states unified into the Prussian-dominated German Empire. After World War I and the German Revolution of 1918–1919, the Empire was replaced by the semi-presidential Weimar Republic. The Nazi seizure of power in 1933 led to the establishment of a dictatorship, World War II, and the Holocaust. After the end of World War II in Europe and a period of Allied occupation, Germany was divided into the Federal Republic of Germany, generally known as West Germany, and the German Democratic Republic, East Germany. The Federal Republic of Germany was a founding member of the European Economic Community and the European Union, while the German Democratic Republic was a communist Eastern Bloc state and member of the Warsaw Pact. After the fall of communism, German reunification saw the former East German states join the Federal Republic of Germany on 3 October 1990—becoming a federal parliamentary republic led by a chancellor.