How did the death of Franz Ferdinand instigate (urge on) the collapse of peace in Europe?

After that death, the Austria-Hungarian empire wanted full military access to the territories of Serbia, under the pretense that they would use it to investigate the murder. Since it was an ultimatum, the Serbians denied them access and Austria-Hungary declared war. Since they were against them, many forces allied with Serbia and wanted to fight against Austria-Hungary and Germany, who were allies in the war. They were joined by many nations such as Russia, USA, Britain, France, Japan, Italy, and many others, while the Axis forces were joined by Bulgaria and the Ottoman Empire.