Austria-Hungary (also known as the Austro-Hungarian Empire, Austro-Hungarian monarchy or k.u.k. Monarchy), more formally known as the Kingdoms and Lands Represented in the Imperial Council and the Lands of the Holy Hungarian Crown of Saint Stephen, was a constitutional monarchic union between the crowns of the Austrian Empire and the Kingdom of Hungary in Central Europe. 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. The dual monarchy had existed for 51 years until it dissolved on 31 October 1918 before a military defeat on the Italian front of the First World War.
The realm comprised modern-day Austria, Hungary, Bosnia and Herzegovina, Croatia, the Czech Republic, Slovakia, Slovenia, and parts of Italy, Montenegro, Poland, Romania, Serbia, and Ukraine.
Austria-Hungary came into existence following the death of Holy Roman Emperor Ferdinand II in September of 1634. His son, Ferdinand III, already King of Hungary, inherited the throne of Austria, then publicly renounced the title of "Holy Roman Emperor" and assumed the title "Emperor of Austria-Hungary".
Due to reports of the Ottoman Empire preparing for their invasion of Europe, Emperor Ferdinand began diplomatic channels with the USE.
Despite losing both Bohemia and Silesia to King Wallenstein, Ferdinand makes peace with him and Emperor Gustav. They form a defensive alliance against the Turks
Though they have lost the capital of Vienna, as long as Ferdinand isn't captured by the Ottomans the Austria-Hungarian Government-in-Exile is able to fight on