The Austria-Hungarian Empire was a large nation in Central Europe comprised of all of OTL Austria, Hungary, Czech Republic, Slovakia, and parts of Romania and Bulgaria. They gained their sovereignty after the Austrian Empire annexed Hungary following a short war in 1876. The Austrians then proceeded to integrate their new territory into their new nation with a sweeping modernization program proposed by Archduke Gregory III. They were wildly successful, and Austria-Hungary remains a dominant power in Central Europe.