When did hostilities start in World War 1?

Hostilities in World War I began on July 28, 1914, when Austria-Hungary declared war on Serbia following the assassination of Archduke Franz Ferdinand. This declaration set off a chain reaction of alliances and mobilizations, leading to widespread conflict across Europe. Within weeks, major powers like Germany, Russia, France, and the United Kingdom were drawn into the war, marking the start of a devastating global conflict.