Answer:
the assassination of Austrian Archduke Francis Ferdinand in Sarajevo.
Step-by-step explanation:
In simple words, The execution of Archduke Franz Ferdinand of Austria-Hungary was the direct source of World War I, which brought the aforesaid components into play (coalitions, colonialism, militarization, and patriotism). The Archduke was assassinated by the Black Hand, a Serbian nationalist terrorist organisation, in June 1914.