Various Germanic tribes have occupied what is now northern Germany and southern Scandinavia since classical antiquity. A region named Germania was documented by the Romans before AD 100. During the Migration Period that coincided with the decline of the Roman Empire, the Germanic tribes expanded southward and established kingdoms throughout much of Europe. 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. The rise of Pan-Germanism inside the German Confederation, which had been occupied by France during the Napoleonic Wars, resulted in the unification of most of the German states in 1871 into the Prussian-dominated German Empire. As a result of the military defeat in World War I, and the German Revolution of 1918–1919, the Empire was replaced by the parliamentary Weimar Republic. The establishment of the Third Reich, or Nazi Regime, in 1933 eventually led to World War II and the Holocaust. In 1945, the remnants of the Nazi regime surrendered to the Allied Powers. Over the next few years, Germany lost some additional territory and was divided by the victors Allied occupation zones, and evolved into two states, East Germany and West Germany. On 3 October 1990, the country was reunified, regaining full sovereignty about six months later.