- June 28: Archduke Franz Ferdinand of Austria is assassinated by a Serbian nationalist in Sarajevo, the provincial capital of Bosnia-Herzegovina (formally annexed by Austria-Hungary in 1908).
- July 28: Austria-Hungary declares war on Serbia, marking the official beginning of World War I.
- August 4: Germany invades Belgium, prompting Great Britain to declare war on Germany.
- August 5: The United States declares its neutrality in the war.
1915:
- May 7: The British passenger liner RMS Lusitania is sunk by a German U-boat, killing 1,198 people, including 128 Americans.
- September 15: The United States sends a note to Germany warning that it will hold Germany responsible for any further loss of American lives in the war zone.
1916:
- March 24: The French passenger ship SS Sussex is sunk by a German U-boat, injuring several Americans.
- April 18: President Woodrow Wilson sends a second note to Germany, warning that the United States will break diplomatic relations if Germany does not stop attacking merchant ships without warning.
- May 4: Germany issues the Sussex Pledge, promising to stop attacking merchant ships without warning.
- November 7: Woodrow Wilson is re-elected president, campaigning on the slogan "He kept us out of war."
1917:
- January 31: Germany resumes unrestricted submarine warfare in the Atlantic, despite its Sussex Pledge.
- February 3: The United States severs diplomatic relations with Germany.
- March 12: The British liner SS Laconia is sunk by a German U-boat, killing two Americans.
- April 2: President Woodrow Wilson asks Congress for a declaration of war against Germany.
- April 6: The United States declares war on Germany, entering World War I.