Key events surrounding the start of World War I include the assassination of Archduke Franz Ferdinand of Austria on June 28, 1914, which triggered a series of alliances and escalatory actions. Following the assassination, Austria-Hungary declared war on Serbia, leading Russia to mobilize in defense of Serbia. This action pulled multiple countries into the conflict due to existing alliances, resulting in a cascade of declarations of war. The July and August of 1914 saw major powers align into the Central and Allied Powers, ultimately starting a war that would engulf Europe and lead to significant loss of life and geopolitical shifts.