World War I officially started on July 28, 1914, following the assassination of Archduke Franz Ferdinand of Austria. This act triggered a complex web of alliances, leading to a conflict that escalated rapidly. Major powers like Germany, Austria-Hungary, Russia, France, and later the United Kingdom and Italy engaged in a war that would engulf much of Europe and eventually the world. The war was marked by trench warfare, significant military innovations, and unprecedented casualties. The resultant Treaty of Versailles in 1919 sought to address the war's aftermath but ultimately sowed the seeds for future conflicts, including World War II, showcasing the far-reaching consequences of the war.