Answer:
assassination of Archduke Franz Ferdinand of Austria-Hungary.
Step-by-step explanation:
These are the causes of tension in Europe that led to world war one
European Expansionism.
Serbian Nationalism.
The Assassination of Franz Ferdinand.
Conflicts over Alliances.
The Blank Check Assurance: Conspired Plans of Germany and Austria-Hungary.
Germany Millenarianism
These nations were driven by the ideologies of the day: imperialism, which encouraged territorial expansion and empire building; militarism, which promoted a policy of war and the build-up of armies and navies; and nationalism, which focused on unity and loyalty within countries.
The immediate cause of World War I that made the aforementioned items come into play (alliances, imperialism, militarism, nationalism) was the assassination of Archduke Franz Ferdinand of Austria-Hungary. In June 1914, a Serbian-nationalist terrorist group called the Black Hand sent groups to assassinate the Archduke.