In OTL, at 28. June 1914, Archduke Franz Ferdinand d'Este went to Sarajevo. Organization called Black Hand prepared assassination, but the first six assassins failed. Seventh assassin, Serbian student Gavrilo Princip, thought the assassination was cancelled. Archduke Franz Ferdinand wanted to go to hospital, visit the victims of attempted assassination of Nedeljko Čabrinović. They didn't want to go through center of city, but they forgot to tell the driver. So they went around the place, where Princip was having snack. He shot the Archduke and his wife, and actually caused the First World War.
But what if they told driver they changed the way?
In this timeline they told the driver and didn't meet Princip.
Government of Austro-Hungary just set up secret police in Bosnia and Serbia. They found the Black Hand and Serbia was forced to give them to Austria. After death of Franz Joseph I., Franz Ferdinand tried to federalize the Empire. But Hungarians didn't want federalization, because they would have to give parts of their land to other ethnic groups, and declared independence. That caused Austrian civil war, which increased tension in world and almost grown to world war. Hungarians were defeated and United states of Greater Austria were formed.
But World War happened. It was caused by Bulgaria, which wanted some lands with Bulgarian majority from Romania. The Entente was really close to defeat, but they finally won the war.