Vienna.
Astria wanted to get revenge on Serbia for killing franz Ferdinand and his wife, who were murderd when they took the wrong turn on the way to seeing their new army
last time i checked, it seemed it was roughly 48 million... i could be wrong though
The Austro/Hungarian Empire was Germany's ally in WW1
A serbian student killed the archduke of Austria-Hungary, Franz Ferdinand. This event was the trigger that caused the outbreak of WWI