1917 was a crucial year in the war. The United States had followed a policy of neutrality in the war, feeling it was a European conflict. However, during the course of the war many Americans had died on board British ocean liners sunk by the Germans, leading to anti-German feelings in the U.S. There had also been incidents of sabotage on American soil, including the Black Tom explosion. What finally led to American involvement in the war, however, was the discovery of the Zimmermann Telegram, in which Germany offered to help Mexico conquer part of the United States if it formed an alliance with Germany. In April, the U.S. declared war on Germany. The same year the U.S. entered the war, Russia withdrew. After the deaths of many Russian soldiers and hunger in Russia, a revolution occurred against the Czar, Nicholas II. Nicholas abdicated and a Liberal provisional government was set up. In October, Russian communists, led by Vladimir Lenin rose up against the government, resulting in a civil war. Eventually, the communists won and Lenin became premier. Feeling World War I was a capitalist conflict, Lenin signed a peace treaty with Germany in which it gave up a great deal of its Central and Eastern European lands.