Why did the United States become involved in World War I?

Germany attempted to instigate a conflict between the United States and Canada to draw American attention away from Europe.

It came in part from the unrestricted submarine warfare Germany waged on all nations that traded with its enemies.

The United States entered the war as a requirement of the American-French alliance from the Revolutionary War.

An attempted assassination of President Wilson by a German-born American convinced the United States to enter the war.

ONE ANSWER

The United States became involved in World War I primarily due to the unrestricted submarine warfare and sinking of American ships by Germany. This, along with other factors such as economic interests and desired influence on post-war peace agreements, led President Woodrow Wilson to declare war on Germany in April 1917.