What led to the start of World War I?

The assassination of Archduke Franz Ferdinand is widely regarded as the immediate catalyst that triggered the outbreak of World War I. On June 28, 1914, Ferdinand, heir to the Austro-Hungarian throne, was assassinated by Gavrilo Princip, a member of a nationalist group seeking to end Austro-Hungarian rule over Bosnia. This event set off a chain reaction of political alliances and militaristic responses among the major powers of Europe.

In the aftermath of the assassination, Austria-Hungary issued an ultimatum to Serbia, leading to Serbia's partial acceptance of the demands and Austria-Hungary's subsequent declaration of war on July 28, 1914. This declaration activated a complex web of alliances involving countries such as Germany, Russia, and France, ultimately expanding the conflict into a full-scale global war. The assassination directly linked to nationalistic tensions in the Balkans and the prevailing militarism of the time created a volatile environment ready for war.

While the other options listed are significant events related to World War I, they occurred either during or after the war's initial outbreak. The Treaty of Versailles, for example, was signed in 1919 to officially end the war, and the sinking of the Lusitania