1. Archduke Franz Ferdinand is assassinated in Sarajevo.
2. 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.
3. Germany invades Belgium, beginning World War I.
4. A German submarine sinks the passenger liner Lusitania. The ship carries 1,198 people, 128 of them Americans.
5. The British employ the first tanks ever used in battle, at Delville Wood. Although they are useful at breaking through barbed wire and clearing a path for the infantry, tanks are still primitive and they fail to be the decisive weapon, as their designers thought they would be.
