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

This revolution is what established the government form of communism in Russia, which the United States was directly opposed to. As a result of the revolution, Russia signed the treaty of Bretsk-Litovsk with the Germany, allowing them to leave the war. The United States realized that without its help, England, France, and their allies were going to lose the war. This was one of the major factors in the United States' decision to join WWI, and it could be considered a fight for democracy because of a communist revolution being the cause for Russia to leave the war.
Another reason the United States joined the war as a fight for democracy was Woodrow Wilson's goal to have peace without victory, which meant that he hoped to not claim a total victory as had occurred in previous wars where one country would drastically harm another either in the taking of land or economically. Wilson proposed the League of Nations along with this, which could be considered a precursor to the United Nations, even though it was much weaker with much smaller membership.