Answer:
The Russian Revolution started. It was a period of political and social revolution across the territory of the Russian Empire, commencing with the abolition of the monarchy in 1917, and concluding in 1923 after the Bolshevik establishment of the Soviet Union, including national states of Ukraine, Azebaijan and others, and end of the Civil War.
It began during the First World War, with the February Revolution that was focused in and around Petrograd (now Saint Petersburg), the capital of Russia at that time.
The Russian Revolution was one of the factors that moved the United States to enter the war. However, the main factor for the United States to enter the war was because of the Germans' decision to resume the policy of unrestricted submarine warfare, and the so-called "Zimmerman telegram," intercepted by the British, in which Germany floated the idea of an alliance with Mexico.
