Why was Archduke Franz Ferdinand Assassinated and how was this a catalyst for WW1?

Archduke Franz Ferdinand was the heir to the Austro-Hungarian Empire. Austria-Hungary had annexed the Balkans in 1908 and in turn infuriated the Serbian nationals there. Thanks to this annexation, many nationalist groups had been created as they believed they should be allowed to join the new independent Serbian nation. On the day that he was assassinated, Franz Ferdinand had travelled to Sarajevo in order to inspect his troops there. On June 28th, 1914, the archduke and his wife, Sophie, travelled in an open top car through the streets of Sarajevo. It was at this point that a Serbian nationalist from the Black Hand Gang, Nedjelko Cabrinovic, threw a bomb into the car. The bomb hit the back of the vehicle and missed the Archduke, hitting and wounding bystanders. The archduke and his wife were taken to safety, however, he decided that they should go visit these wounded people in the hospital. On the way to visit these people, his driver took a wrong turn, right into Franzjosefstrasse, where another member of the Black Hand Gang, Gavrilo Princip had been buying lunch. He took his opportunity at fired at the archduke and his wife, killing them both. This assassination set off a chain of events which descended into war. The Austria-Hungarian government blamed Serbia for the attacks and sent them an ultimatum. They were to admit the clauses of a document sent to them. Serbia accepted all but one and Austria declared war on Serbia on July 28th, 1914. Russia supported Serbia and went to war to protect them after Kaiser Wilhelm and Germany supported the Austrian Cause. France and Britain joined the cause after a failed Schlieffen plan by Kaiser Wilhelm.