Describe the Sarajevo incident of the First World War.

The assassination of Franz Ferdinand, the heir to the Habsburg throne, and , by incident, duchess Sophie , by Gavrilo Princip in Sarajevo on 28th June 1914 triggered the First World War.
There had been trouble at the start of his royal tour of Sarajevo when another car in his entourage was hit by a grenade and an Austrian officer had been injured. Clearly, Sarajevo was a dangerous place to be.
However, Franz Ferdinand wanted to demonstrate that his family was in control of Sarajevo and to have stopped the tour would have been seen as a sign of weakness by those who did not want Bosnia and Sarajevo ruled by the Austrians.
Franzordered that his route through Sarajevo be changed at the last minute as he wanted to see the injured officer in hospital. Unfortunately, his driver did not fully understand his instructions and got lost.
Stopping to check where he was, the driver attempted to reverse out on to the main street. By bad luck, he stopped right by a man called Gavrilo Princip. He was a member of the Black Hand Gang which wanted to rid Bosnia of Austrian rule. He had also been behind the grenade throwing and was now trying to disguise himself among the many people who lined the streets fearing the police might arrest him. Not believing his luck, Princip pulled out the revolver he had on him and shot Franz and his wife. Both died as a result.

The assassination of Archduke Franz Ferdinand, heir to the Austro-Hungarian Empire, while visiting Sarajevo in Bosnia is widely acknowledged to have been the trigger cause of the First World War. While many other elements combined to push Europe into war, it was this assassination which was the straw that broke the camel's back.
In June 1914, Franz Ferdinand was visiting Sarajevo, which was at that time part of the Austrian Empire. An independence movement was brewing in Bosnia, however, and although Ferdinand was warned of possible violence, he opted to go ahead with his state visit, traveling in an open car. In part, his determination to continue with the visit, despite the violence in Bosnia, stemmed from a desire to show strength and stand up to those who opposed his family's rule.
By chance, Franz Ferdinand asked to take a different route than planned through Sarajevo, because he wanted to visit an officer who had been hospitalized by an earlier grenade attack on a car. This change of route brought the Archduke directly into the path of Black Hand member Gavrilo Princip, who was able to shoot and kill both the Archduke and his wife while their car was stopped. This led the Austrians to determine that Serbia was to blame for financing the Black Hand group and thus began the First World War.
https://www.historylearningsite.co.uk/world-war-one/causes-of-world-war-one/assassination-at-sarajevo/