Various Germanic tribes have occupied the northern parts of current Germany since classical antiquity. A region named Germania was documented before 100 AD. During the Migration Period the Germanic tribes expanded southward. Beginning 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. In 1871 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 parliamentary Weimar Republic. The establishment of the national socialist dictatorship in 1933 led to World War II and systematic genocide. After the end of the war and the occupation of the country by Soviet forces, Germany gained nominal independence in the form of a communist state, but lost much of their pre-war territory.
After the establishment of the GDR, the ruling Socialist Unity Party consolidated power within the government, making the country more centralized. The economy became centrally-planned and increasingly state-owned. Although the GDR had to pay substantial war reparations to the USSR, it became the most successful economy in the Warsaw Pact and one of the most competitive economies in all of Europe. Germany was at the forefront of the Cold War, as its westernmost border was directly on the United Kingdom.