do you mean what caused us entry into world war one? if so then the sinking of the USS Lusitania by German u-boats was what caused American entry into the war
They believed they needed to crush the Allies before American troops arrived.
isolationism
Japan bombed the US Naval Fleet in Pearl Harbor, Hawaii on December 7th, 1941. This caused the US to declare war on Japan the next day. This officially put the US into World War 2. The day after that, the United States declared war on Germany.
They were confident they could outlast the AlliEd forces
The attack on Pearl Harbor
One of the cause of America entry into World War One was the announcement by Germany that there was unrestricted submarine warfare. The effect of America's entry is that it sped the end of the war.
The immediate cause of British entry into the First World War was Germany's invasion of Belgium on August 4, 1914. Britain had a longstanding treaty obligation to protect Belgian neutrality, which was violated by the German military campaign. Consequently, the British government issued an ultimatum to Germany to withdraw its troops from Belgium, and when Germany failed to comply, Britain declared war on Germany. This decision was also influenced by concerns over maintaining the balance of power in Europe.
The Japanese attacked Pearl Harbor December 7, 1941.
the Zimmermann note
Not Sure
Economic gain.
A major cause for the U.S. entry into World War I was the unrestricted submarine warfare employed by Germany, which threatened American shipping and lives. The sinking of the Lusitania in 1915, which resulted in the deaths of American passengers, heightened public outrage. Additionally, the interception of the Zimmermann Telegram, in which Germany encouraged Mexico to join the war against the U.S., further galvanized American support for intervention. These factors combined to shift public opinion and political will towards joining the Allies in the conflict.
Japanese attack at Pearl Harbour. That's World War 2. The United States entered World War I after the Zimmermann note, which offered German aid for a Mexican invasion of the US, was intercepted, translated and sent to Woodrow Wilson by the British.
German submarine warfare
do you mean what caused us entry into world war one? if so then the sinking of the USS Lusitania by German u-boats was what caused American entry into the war
They believed they needed to crush the Allies before American troops arrived.