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Submarine Warfare and the Lusitania

  • There were unauthorized German submarines along the US East coast. Germany's resumption of unrestricted submarine warfare in the spring of 1917 provided the final straw for US politicians, and America declared war.
  • The first and foremost answer would be the sinking of the Lusitania, an British cruise/transport ship, bound for Britain from New York. The German U-boat ring sought to sink all supply ships headed for Britain in order to starve the island. It sank the Lusitania as part of its efforts. 1195 people died, including 128 Americans.
  • The Lusitania's sinking was the biggest influence on the American decision to enter the war. German submarine warfare (the Lusitania is included in this) sunk many ships over several years.
  • Had it not been for the Lusitania, the US would have stayed out of the War.


Some say the "bankers" were involved.

  • The U.S. had huge economic investments with the British and French. If they were to lose, then they would not be able to pay the U.S. debt back (amounting to about two billion dollars while Germany only borrowed a mere 27 million).
  • If Allies could not pay back all the loans made to them by the American bankers, the US's economy could collapse.
  • France and England were financing their war with US loans. In addition, they were buying massive amounts of arms from the US on credit. The US wanted to make sure that it got paid back. Germany also purchased arms, but in a much more limited fashion.


  • Propaganda from both sides influenced the American decision.
  • Woodrow Wilson did not want to go to war but when Teddy Roosevelt decided to run for another term, Wilson felt threatened and announced that there would be a preparedness program and possibly that the country would go to war.
  • By entering the war, the US got to flex its muscles on the world stage and establish itself as a world power.
  • After both sides of the Mexican civil war demanded that our troops leave and public opinion badly swayed against US intervention in Mexico, Wilson had no choice but to withdraw. By having the threat of Germany helping Mexico fight back against him, Wilson knew he had to take action. He couldn't go back into Mexico because the American people would not allow it. He really had no beef with Germany, he just wanted to save face before Mexico could fight back.


  • President Wilson wanted to make the world safe for democracy ("Wilson's War Address to Congress").
  • It was partly for idealistic reasons (propaganda was not seen as an evil until after the Great War). The occupation of Belgium and the sinking of the Lusitania changed a lot people's minds in the US about Germany.
  • There was more to it than just the submarine warfare and the sinking of the Lusitania although those were the formal and legalistic reasons for declaring war. I think that over time a moral sense had developed that Britain and France were fighting the good fight for freedom against a genuine evil. If that sense had not existed I think the US would have let the Lusitania pass. As it was, it was nearly two years after she was sunk that we finally did declare war.

Zimmerman Telegram

Other points influenced entrance to the war, but the Zimmerman Telegram (sometimes called the "Zimmerman note" or "Zimmerman telegraph") finally pushed the US to war. The Zimmerman Telegram was sent from the German foreign secretary to the German Ambassador to Mexico. It stated the following:

  • On the first of February, 1917, submarine warfare will be reinstated unrestrictively.
  • The US has to stay neutral.
  • Germany proposes an alliance with Mexico on the following basis: If the US goes to war, Mexico must fight on the home front in an financially supported alliance with Germany; If Mexico agrees to fight, they will reconquer New Mexico, Texas and Arizona.

The telegraph was intercepted by British Intelligence and transmitted to the American government by the Brits.

This infuriated Americans. It was the same sort of alliance that plunged Europe into war.

Other WikiAnswers Contributors agree:

  • The clincher was "discovery" of the Zimmerman Telegram (it was de-coded by the British and forwarded to US diplomats; with obvious self-interest on the part of the Brits).

Read more: How_did_the_US_get_involved_in_World_War_1

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Q: Who made the decision to enter World War 1?
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Related questions

Was it a good decision for the US to enter the World War 1?


What US sinking ships sealed the US decision to enter world war 1?

The Titanic

The major reason for America's decision to enter World War 1?

unrestricted submarine warfare

How did Wilson's belief in world peace effect his decision to enter the war?

Hitler's dog pooped on his lawn.

Was a major factor in the decision of the US to enter World War 1?

Germany's unrestricted submarine warfare

How did the zimmerman note and lusitania led to world war 1?

They did not lead to war; they were part of the war. They were, however, factors in the United States' decision to enter the war.

Was it beneficial to the US to enter World War 2?

The United States would not make a decision to enter war unless there was a benefit to be gained...That being said, aiding in WWII was morally responsible

How did the Lusitania play a part in the US decision to enter World War 1?

it sunk by a torpedo from U-20, a submarine

Who made a decision to use an atomic bomb to end World War 2?

Harry Truman

What event made Americans willing to enter World War 2?

pearl harbour!

Who sent the message that made us enter World War 1?

Arthur Zimmerman

Who were the merchants of death in World War 2?

The "Merchants of Death" were the US weapons' suppliers of World War I and World War II that were thought by some people to have dragged the country into "a struggle that was none of its business" by unduly influencing the American decision to enter the War so that they could make a profit off of it. During both World War I and World War II, these manufacturers of armaments made enormous amounts of money by supplying the military with their weapons.