141 The End of World War I
29.4: The End of World War I
29.4.1: American Entry into WWI
The American entry into World War I came in April 1917, after two and a half years of efforts by President Woodrow Wilson to keep the United States neutral.
Learning Objective
Explain why the United States entered WWI
Key Points
- After World War I began in 1914, the United States proclaimed a policy of strict neutrality, with President Wilson trying to broker peace.
- American public opinion was strongly divided, with most Americans until early 1917 supporting the United States staying out of the war.
- When the German U-boat U-20 sank the British liner Lusitania on May 7, 1915, with 128 U.S. citizens aboard, Wilson demanded an end to attacks on passenger ships as they were in violation of international law and of human rights; Germany complied.
- Wilson came under pressure from war hawks led by former president Theodore Roosevelt, who denounced German acts as “piracy.” Public opinion, angry over the sinking of the Lusitania, began to sway in favor of entering the war.
- In January 1917, Germany resumed unrestricted submarine warfare against their 19155 agreement with the U.S.
- The German Foreign minister, Arthur Zimmermann, invited revolution-torn Mexico to join the war as Germany’s ally against the United States in the Zimmermann Telegram. This was intercepted by the British and given to the Americans, who saw it as a cause for war.
- The United States declared war on the German Empire on April 6, 1917, and immediately began sending troops to France.
Key Terms
- casus belli
- A Latin expression meaning “an act or event that provokes or is used to justify war” (literally, “a case of war”). It involves direct offenses or threats against the nation declaring the war, whereas a casus foederis involves offenses or threats against its ally—usually one bound by a mutual defense pact. Either may be considered an act of war.
- Zimmermann Telegram
- A secret diplomatic communication issued from the German Foreign Office in January 1917 that proposed a military alliance between Germany and Mexico in the event of the United States entering World War I against Germany. The proposal was intercepted and decoded by British intelligence. Revelation of the contents enraged American public opinion, especially after the German Foreign Secretary Arthur Zimmermann publicly admitted the telegram was genuine on March 3, and helped generate support for the United States declaration of war on Germany in April.
- sinking of the Lusitania
- On May 7, 1915, during the First World War, as Germany waged submarine warfare against the United Kingdom of Great Britain and Ireland, the Lusitania was identified and torpedoed by the German U-boat U-20 and sank in 18 minutes. The vessel went down 11 miles off the Old Head of Kinsale, Ireland, killing 1,198 and leaving 761 survivors. The sinking turned public opinion in many countries against Germany, contributed to the American entry into World