What happens in Russia in 1917 that led the United States to justify its involvement in the World War I as a fight for democracy?

United States formed the allied forces under the Head of Woodrow Wilson who rejected to join hands with the despotic Tsar as an associate and agreed to extend technical assistance to Kerensky of Russia.

Russian Revolution became unpopular because Bolsheviks were a group of revolutionaries who are peasants and they revolted against the tyrannical rule Tsar II. Internal revolts ended Russian revolution.

US decided to involve in World War I because Germany started to round up the US ships which transported war munitions.