The United States entered WWI for two main reasons - the sinking of the Lusitania and the Zimmerman Telegram. Of course, the U.S. also entered the war to assist its allies as well as fight for noble causes such as democracy and freedom, but these were not the main reasons...
The United States entered WWI for two main reasons - the sinking of the Lusitania and the Zimmerman Telegram. Of course, the U.S. also entered the war to assist its allies as well as fight for noble causes such as democracy and freedom, but these were not the main reasons that ultimately led to the U.S. entering the war. Some Americans were in favor of the U.S. getting involved, but many were not and wanted the U.S. to remain neutral. As we know, that didn't exactly happen.
The United States entered WWI near the end of the war. Germany had begun unrestricted naval warfare, meaning that the Germans were sinking any and all non-German ships regardless of who was on them. On May 7, 1915, Germany sunk the Lusitania, a British passenger ship. 1,200 people died as a result, 128 of which were Americans. This enraged Americans and they demanded that Germany let ships pass in peace.
The "final straw" was the Zimmerman Telegram. Zimmerman was a German official. He sent a message to Mexican officials saying that if they would help Germany win the war, Germany would help Mexico regain land that they had lost to the United States years ago. U.S. officials intercepted the telegram. While not directly declaring war on the United States, the overall message was that Germany and Mexico would declare war on the U.S. if they won. Obviously, that wasn't ideal for the U.S., so President Wilson declared war on Germany and assisted Britain and its allies with winning the war against Germany.
While many Americans felt that the U.S. had no business being involved in a European war, it is unknown what might have happened if Germany had won and then attacked the United States. The American forces played a big part in helping to end WWI, and not only European history but American history, too, might have been different if the U.S. had not entered WWI.