Question

what happened to austrian empire after first world war

Answer 1

Austria-Hungary was split between Austrian and Hungarian administrations, and from my understanding the Hungarian side, amidst the turmoil of a disastrous war and heightened ethnic nationalism because of it, distanced itself from Austria. The two were competitors for power and focus at the best of times. It was a heady time to declare independence across Europe as the losing countries' propaganda machines collapsed and traditional loyalties crumbled - even little Liechtenstein, a mere duchy, broke away to avoid the ramifications of defeat. The Habsburgs made a couple appeals for Hungary to rejoin Austria but these were laughed at. I think they were quietly deposed in Austria.

Reduced to a rump state there was little Austria could do on the international stage. There were two communist uprisings in Vienna in the early-mid twenties, plus Hungarian and German revolutions, so unsurprisingly anti-communism was top of the government's agenda for a while.
the division was not of the Allies design - they were too late for that. They could only try to mediate the new borders (so Italy lost out in the Balkans. They were probably unwilling to punish Austria even more territoriality (except Italy again), as it was clearly no longer a great power and was up for influencing).