When did the Austro-Hungarian empire split and why?

The Austrian-Hungarian empire was split up by other European countries during the treaty at the end of World War 1. Other factors may have contributed to the other nations' decision to break them up, because they experienced disintegration and revolution, as well as the fear of another war caused by Austria-Hungary and Germany. As war weariness took hold of the empire, ethnic groups increasingly sought to achieve their independence. By the time the war ended the Austro-Hungarian Empire was no more. They had been replaced by independent republics of Austria, Hungary, and Czechoslovakia, along with the large monarchical state called Yugoslavia.

The Austro-Hungarian Empire actually split up in October 1918, before the war even ended; it was not split up by other European countries. The proof being that there wasn't one single treaty ending the war for Austria-Hungary- there were actually two major treaties (Saint-Germain with Austria and Trianon with Hungary) and then several "Minority Treaties" with the new countries that had emerged so that they could join the League of Nations.