- German announcement of unrestricted submarine warfare in 1917.
Underlying causes:
- Britain’s blockade of Germany disrupted trade and caused shortages in Germany, leading to increased support for unrestricted submarine warfare.
- Loss of American lives due to German submarine attacks (e.g., Sinking of the Lusitania).
- Zimmermann Telegram: a telegram sent by the German Foreign Secretary revealing a plan to form an alliance with Mexico against the United States.
- American economic ties to Britain and France.
- Growing public outrage over German atrocities, such as the rape of Belgium and the use of chemical weapons.
- American President Woodrow Wilson’s belief in the importance of democracy and the need to uphold international law.