How did the assassination of Archduke Franz Ferdinand by a Serb lead to World War I? It allowed Russia to ally with Serbia and declare war on Germany.

The alliance between Serbia and Austria-Hungary sparked unrest that stemmed from the failure of the Treaty of Paris.

Alliances forced many countries to go to war in support of either Austria-Hungary or Serbia.

Bismarck’s scheme of secret alliances against Serbia provoked the assassination and then the war.