Austria was overrun in Pre-Roman times by various tribes, including the Celts. After the fall of the Roman Empire, of which Austria was part, the area was invaded by Bavarians and Slavic Avars. Charlemagne conquered the area in 788 and encouraged colonization and Christianity. In 1252, Ottokar, king of Bohemia, gained possession, only to lose the territories to Rudolf of Hapsburg in 1278. Thereafter, until World War I, Austria's history was largely that of its ruling house, the Hapsburgs.
Austria emerged from the Congress of Vienna in 1815 as the continent's dominant power. The Ausgleich of 1867 provided for a dual sovereignty, the empire of Austria and the kingdom of Hungary, under Franz Joseph I, who ruled until his death on Nov. 21, 1916. The Austrian-Hungarian minority rule of this immensely diverse empire, which included German, Czech, Romanian, Serbian, and many other lands, became increasingly difficult in an age of emerging nationalist movements. When Archduke Francis Ferdinand was assassinated by a Serbian nationalist in Sarajevo in 1914, World War I, as well as the destruction of the Austro-Hungarian Empire, began.
During World War I, Austria-Hungary was one of the Central powers with Germany, Bulgaria, and Turkey, and the conflict left the country in political chaos and economic ruin. Austria, shorn of Hungary, was proclaimed a republic in 1918, and the monarchy was dissolved in 1919. A parliamentary democracy was set up by the constitution of Nov. 10, 1920. To check the power of Nazis advocating union with Germany, Chancellor Engelbert Dolfuss in 1933 established a dictatorship, but he was assassinated by the Nazis on July 25, 1934. Kurt von Schuschnigg, his successor, struggled to keep Austria independent, but on March 12, 1938, German troops occupied the country, and Hitler proclaimed its Anschluss (union) with Germany, annexing it to the Third Reich.