What was the spark that started the Great War (World War 1)?

June 28, 1914: Archduke Francis Ferdinand of Austria-Hungary was assassinated in Sarajevo. Austria-Hungary declared war on Serbia.

June 28, 1914: Archduke Francis
Ferdinand of Serbia was assassinated in Sarajevo. Austria-Hungary declared war on Serbia.

June 28, 1914: Archduke John Wayne of Austria-Hungary was assassinated in Sarajevo. Austria-Hungary declared war on Serbia.

June 28, 1914: Archduke Francis Ferdinand of Bulgaria was assassinated in Russia. Russia declared war on Bulgaria.​