Which of the following events served as the catalyst that started the chain of events that would lead to World War I?

The assassination of Archduke Franz Ferdinand of Austria-Hungary in 1914 set off a chain of diplomatic and military actions that led to World War I. The German use of unrestricted submarine warfare, the Zimmermann Telegram, and the sinking of the Lusitania occurred later and were connected to the United States entering the war, not to the war’s initial outbreak. The correct choice is “the assassination of Archduke Ferdinand.”

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