Final answer:
The assassination of Archduke Franz Ferdinand of Austria-Hungary on June 28, 1914, was the 'powder keg' event that ignited World War I. It set off a chain of declarations of war that involved all the major European powers and their alliances, escalating the situation into a full-scale global conflict.
Step-by-step explanation:
The Assassination That Ignited World War I
The event referred to as the “powder keg” incident that led to the outbreak of World War I was the assassination of the heir to the Austria-Hungarian throne. On June 28, 1914, Archduke Franz Ferdinand of Austria-Hungary was killed by Gavrilo Princip, a Bosnian Serb nationalist, in Sarajevo. This assassination triggered a series of alliances and agreements among the great powers of Europe to come into play. Austria-Hungary, with the backing of Germany, declared war on Serbia. This declaration caused a domino effect involving many European nations due to existing treaties and alliances, which eventually escalated into the global conflict known as World War I.
After the assassination, Austria-Hungary's declaration of war on Serbia prompted Russia to come to Serbia’s defense, which in turn led Germany to declare war on Russia and its ally, France. The German invasion of Belgium caused Great Britain to join the war against Germany. With the major European powers now at war, the conflict quickly spread as colonies and allied nations around the world were drawn into the fray, escalating a regional assassination into a global cataclysm.