America joined the side of the Allies to secure their victory because in the case that they lost, the wouldn't be able to pay America back.
The US entered the war for a variety of reasons
One of the main reasons the US entered World War I on the side of the allies was because the Germans had sunk the Lusitania, a passenger ship containing many Americans.
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Canada
Because they wanted to win !
The US entered the war on April 6,1917
the US entered the WW2 when the Japanese bombed Pearl Harbour
The US transported supplies to the Allies using merchant and passenger ships carrying United States citizens. This was why the German U-boats attacked these ships and were one of the reasons the US entered the war.
The sinking of the Lusitania was a big one.
The Japanese attack of Pearl harbor
1. Germans sank many of their merchant ships before the US entered the war with the their u-boats2. Germans sent a coded message to Mexico that urged Mexico to invade US that British code breakers cracked and sent to the US.
The United States entered the war for many reasons. The number one reason was that the Germans were sinking neutral ships, including U.S. ships and killing Americans.