Final answer:
The assassination of the Archduke Franz Ferdinand triggered World War I due to its impact on the alliances and mobilization of armies.
Step-by-step explanation:
The assassination of the Archduke Franz Ferdinand of Austria on June 28, 1914, played a significant role in triggering World War I. The event took place in Sarajevo, Bosnia, and was carried out by a Serbian nationalist. This assassination led to a chain reaction of events, including Austria-Hungary's ultimatum to Serbia, the mobilization of armies, and the declaration of war by various countries involved in the complex system of alliances at the time.
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