Final answer:
In 1917, the United States entered World War I while Russia withdrew from the conflict after the Russian Revolution and the collapse of the Romanov Dynasty.
Step-by-step explanation:
In 1917, the United States entered World War I while Russia withdrew from the conflict. This happened after a series of events, including the Russian Revolution and the collapse of the Romanov Dynasty. The revolutionaries in Russia wanted to end their country's participation in the war and focus on building a new Soviet Union.