We carefully reviewed the causes of WWI:

1) By 1914, Europe was a delicate house of cards - a system of very complex alliances.
2) Ethnic Tensions in the Balkan Peninsula, the "powder keg of Europe"...
3) Germany's practice of unrestricted submarine warfare...
4) The sinking of British passenger ocean liner the Lusitania, by a German u-boat in 1915...
5) The Zimmerman Telegram - 1917...
6) The assassination of Archduke Franz Ferdinand - 1914...

We began to discuss how the Russian Revolution of 1917 impacted WWI and the U.S. decision to enter the war. After three years of fighting on the front line with Germany on the eastern front, the Russian populace rebelled against Czar Nicholas II. Russia physically withdrew from WWI due to heavy casualties and political turmoil and rebellion resulting in the overthrow of the Czar and replacing Russian aristocratic rule with a Russian "provisional government" that may have supported a constitutional monarchy. However, the provisional government will be overthrown by communists in the Bolshevik Revolution in 1918.

At any rate, with Russia withdrawn from WWI and the national furor over the Zimmerman Telegram, sent from Germany to Mexico - intercepted by Great Britain and presented to the U.S. - President Woodrow Wilson made the difficult decision to enter the U.S. in WWI.