The U.S. joined WWI because of what two events?
Actually, there are more than two events. British and French releasing anti-German propaganda in the United States played a role. Also, the United States loaned the Allies millions of dollars to fight the war and if the Allies lost, then the money would not be repaid.
The main reasons that America entered the war were that Germany resumed unrestricted submarine warfare against Britain and the leak of the Zimmerman note. Germany waged unrestricted submarine warfare as early as 1915, then 128 Americans died on the British liner Lusitania when it was sunk in May of that year. While it was carrying munitions for the Allied war effort in its hold, Wilson called this an attack against innocent civilians, and Germany issued an apology, paid an indemnity, and promised not to do it again. By early 1917, German war planners realized that their window of opportunity for winning the war was closing, so they resumed unrestricted submarine warfare anyway with the logic that the war would be over before America could be a factor. America declared war in April of that year after a few American merchant ships sank.
As to the Zimmerman note, Arthur Zimmerman of the German Foreign Service in Mexico wanted to distract America from the European war, so he devised a scheme where Germany would help Mexico in a war against America in return for Mexico gaining back the land it lost during the Mexican war in 1848. This was still in the planning stages when British intelligence intercepted the telegram and sent it to the American government, where it was quickly released to the press. This stirred up more anti-German sentiment, especially in the West.
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