Why and how did world war 1 began in 1914?

World War I began in 1914 primarily due to a complex web of alliances, nationalism, militarism, and imperial ambitions among European powers. The immediate catalyst was the assassination of Archduke Franz Ferdinand of Austria-Hungary on June 28, 1914, by a Serbian nationalist. This event triggered a series of diplomatic crises and mobilizations, leading Austria-Hungary to declare war on Serbia. The interconnected alliances caused other nations, including Germany, Russia, and France, to become involved, escalating the conflict into a full-scale war.