Austria-Hungary (also known as the Austro-Hungarian Empire, Austro-Hungarian Monarchy or k.u.k. Monarchy, Austro-Hungary, Dual Monarchy, Danube Monarchy) was a constitutional monarchic union, formally known as the Kingdoms and Lands Represented in the Imperial Council and the Lands of the Holy Hungarian Crown of Saint Stephen, between the crowns of the Austrian Empire and the Kingdom of Hungary in Central Europe, which operated from 1867 to October 1918, shortly before the end of World War I. The union was a result of the Austro-Hungarian Compromise of 1867, under which the House of Habsburg agreed to share power with the separate Hungarian government, dividing the territory of the former Austrian Empire between them. The Austrian and the Hungarian lands became independent entities enjoying equal status.
Austria-Hungary was a multinational realm and one of the world’s great powers at the time. Austria-Hungary was geographically the second largest country in Europe after the Russian Empire (621,538 square kilometres (239,977 sq mi)), and the third most populous (after Russia and the German Empire). The Empire built up the fourth largest machine building industry of the world, after the United States, Germany and Britain.
The Austro-Hungarian Empire consisted of two monarchies (Austria and Hungary), and two autonomous countries: Polish Galicia within the Austrian Empire (from 1867) and Croatia within the Kingdom of Hungary (from 1868). Bosnia and Herzegovina and Sandžak-Raška were under Austro-Hungarian military occupation between 1878 and 1908, when the former was fully annexed and the latter was ceded to the Ottoman Empire.
The dual monarchy existed for 51 years until it was dissolved on 31 October 1918 near the end of World War I. Many modern-day nation states have emerged in the territory formerly belonging to the realm. These include Austria, Hungary, Slovenia, Bosnia and Herzegovina, Croatia, the Czech Republic, Slovakia, large parts of Serbia and Romania, and smaller parts of Italy, Montenegro, Poland and Ukraine.