The United States joined World War One in April 1917. However, just under 3 years earlier, in August, 1914 the United States declared its neutrality in the war then engulfing Europe. President Woodrow Wilson, reflecting the views of much of the nation, announced that his country would be “impartial in thought as well as in action”.
This stance soon came under pressure, as the impact of events across the Atlantic were felt in the US. By 1917 isolation had become untenable. In April, Wilson sought the approval of Congress to go to war. Several key factors played a part in this change of course.
These are 5 reasons why the United States joined World War One.
1. The Lusitania
In early 1915, Germany introduced a policy of unrestricted submarine warfare in the Atlantic. This meant U-Boats were hunting and sinking merchant shipping without warning. The RMS Lusitania left New York on 1st May, 1915, bound for Liverpool. On 7th May it was spotted off the coast of Ireland by U-20 and torpedoed. Of 1,962 passengers, 1,198 lost their lives. Among the dead were 128 Americans, causing widespread outrage in the US.
2. The German invasion of Belgium
Following Germany’s invasion of neutral Belgium in 1914, stories began to circulate about atrocities committed against Belgian civilians. These stories, both true and exaggerated, were seized upon for propaganda. So-called “atrocity propaganda” spread far and wide, painting the Germans as a barbaric nation bent on ruthless, indiscriminate destruction. This propaganda was soon sweeping the US, firing anti-German sentiment.
3. American loans
The US had a vested financial interest in the outcome of the war in Europe. American businesses and banks made huge loans to the Allies. If they didn’t win then they were unlikely to get their money back.
4. The reintroduction of unrestricted submarine warfare
Germany resumed unrestricted submarine warfare in 1917. Knowing they risked provoking the United States into joining the war, Germany gambled on defeating the British before the US had a chance to mobilise. During February and March, several US cargo vessels were sunk without warning, resulting in the United States severing diplomatic ties with Berlin.
5. The Zimmerman telegram
In January 1917, the German diplomatic representative in Mexico received a secret telegram penned by German Foreign Secretary Arthur Zimmermann. It proposed a secret alliance between Germany and Mexico, should the United States enter the war. If the Central Powers were to win, Mexico would be free to annex territory in New Mexico, Texas and Arizona. Unfortunately for Germany, the telegram was intercepted by the British and decrypted by Room 40. The British passed the document to Washington and it appeared on the front page of American newspapers on 1st March.
This combination of factors turned public opinion around. On 6 April, the United States declared war on Germany and began to mobilise. The first American troops arrived in Europe in June.