The United States entered world war 1 for a variety of reasons. One of them was the Zimmerman note from Germany to Mexico. A 1917 diplomatic proposal from German Empire for Mexico to join the Central Powers, in the event of the United States entering world war 1. The proposal was intercepted and decode by British intelligence. The other reason was that Germans sunk the Lusitania boat where many Americans were board.
Americans were outraged to learn 128 U.S. civilians were killed in a war in which they were officially neutral. Destroying ships not known to be carrying war materials countered generally accepted international war protocols.
http://www.encyclopedia.com/topic/World_War_I.aspx
The sinking of the Lusitania heightened tensions between the U.S. and Germany and helped sway American opinion in favor of joining the war. At first, president Woodrow Wilson kept United states neutral for two and half years. However, after these tragedies happened they instantly declared war on Germany.
reasons why = this link explains the reasons very clearly.
The US made the right call by entering WWI. After the Lusitania was sunk, and thousands of American lives were lost. America had no other choice because they needed to stand up to German bullying and aggression. Then the Germans sent the Zimmerman Telegram which told Mexico to attack the US. If Germany would of won WWI, and America would’t of entered the war, then what would of stopped Germany from invading America?
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