Archduke Franz Ferdinand is assassinated in Sarajevo. His death is the event that sparks World War I.
Russia mobilizes its vast army to intervene against Austria-Hungary in favor of its ally, Serbia. This move starts a chain reaction that leads to the mobilization of the rest of the European Great Powers, and inevitably to the outbreak of hostilities.
Germany invades Belgium, beginning World War I.
Germany Limits Submarines
The Germans fire shells filled with chlorine gas at Allied lines. This is the first time that large amounts of gas are used in battle, and the result is the near-collapse of the French lines. However, the Germans are unable to take advantage of the breach.
A German submarine sinks the passenger liner Lusitania. The ship carries 1,198 people, 128 of them Americans.
Reacting to international outrage at the sinking of the Lusitania and other neutral passenger lines, Kaiser Wilhelm suspends unrestricted submarine warfare. This is an attempt to keep the United States out of the war, but it severely hampers German efforts to prevent American supplies from reaching France and Britain.