What event triggered the Alliance System leading to World War I?

The assassination of Archduke Franz Ferdinand of Austria-Hungary on June 28, 1914, is widely recognized as the event that triggered the Alliance System leading to World War I. This assassination instigated a series of diplomatic crises and mobilizations between the major European powers, who were bound by various alliances and treaties. Austria-Hungary, with the backing of Germany, issued an ultimatum to Serbia, where the assassin, Gavrilo Princip, was associated with nationalist groups seeking liberation from Austro-Hungarian rule.

Serbia’s response to the ultimatum was deemed insufficient, prompting Austria-Hungary to declare war on Serbia. This declaration activated a complex web of alliances; Russia mobilized in defense of Serbia, prompting Germany to declare war on Russia. France and Britain, being allied with Russia and having certain commitments to defend Belgium’s neutrality, entered the conflict. Thus, the assassination served as the catalyst for a chain reaction that involved multiple nations, bringing about the full-scale war that became World War I.

The other events listed, such as the sinking of the Lusitania, the fall of the Ottoman Empire, and the start of trench warfare, while significant in their respective contexts, occurred later or were consequences of