Germany officially the Federal Republic of Germany is a federal parliamentary republic in west-central Europe. The country consists of 16 states, and its capital and largest city is Berlin. Germany covers an area of 357,021 square kilometres (137,847 sq mi) and has a largely temperate seasonal climate. With 81.8 million inhabitants, it is the most populous member state in the European Union. Germany is one of the major political and economic powers of the European continent and a historic leader in many theoretical and technical fields. A region named Germania, inhabited by several Germanic peoples, was documentedbefore AD 100. During the Migration Period, the Germanic tribes expanded southward and established successor 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 theProtestant Reformation while southern and western parts remained dominated byRoman Catholic denominations, with the two factions clashing in the Thirty Years’ War, marking the beginning of the Catholic–Protestant divide that has characterized German society ever since. Occupied during the Napoleonic Wars, the rise ofPan-Germanism inside the German Confederation resulted in the unification of most of the German states in 1871 into the German Empire, which was Prussiandominated.