Azerbaijan, officially the Republic of Azerbaijan, is a country located at the boundary of Eastern Europe and Western Asia. It is a part of the Caucasus region, and is bounded by the Caspian Sea to the east, Russia to the north, Georgia to the northwest, Armenia and Turkey to the west, and Iran to the south. Baku is the capital and largest city. The Azerbaijan Democratic Republic proclaimed its independence from the Transcaucasian Democratic Federative Republic in 1918 and became the first secular democratic Muslim-majority state, taking its name from the adjacent region of northwestern Iran for political reasons. In 1920, the country was incorporated into the Soviet Union as the Azerbaijan SSR.