When Tsar Nicholas II abdicated his and his son's throne, this left the 4th Duma to become the Provisional Government. The Provisional Government wanted to end the war, but through Russian victory. The Menscheviks, who at the time of the February Revolution controlled the Petrograd Soviet wanted to simply end the war and get out why they could. Lenin adopted a "defeatist" view of the war, hoping that the war would end through Russian defeat. His view was that if Russia lost, it would help the revolutionary movement.

However, once the Bolsheviks seized control of the Petrograd Soviet and the Provisional Government, it became apparent that they needed to get out of the war as easily and simply as possible. Lenin knew that there may be a civil war to fight, and fighting a war with Germany while trying to fight a war internally would prove fatal. The war had already robbed the Provisional Government of its chance at legitimacy and killed its goals of being a democratic government; you can't hold elections if you have a war to fight. Lenin had preached "Peace, Land and Bread" since July and so at the 2nd Congress of Soviet Workers, the Decree of Peace was issued, the one that called for peace and exit from WW1 without ceding land or money to Germany. The reality became the Treaty of Brest-Litovsk(3/1918) where Russian territories in modern Poland, Ukraine and the Balkans were ceded to Germany (that was then ceded to the Allies in the Treaty of Versailles). While the Treat of Brest-Litovsk was a contradiction to the "no annexations" part of the Peace Decree, it was a necessary evil to give the Bolsheviks the breathing room to fight the White Army.

I love how people are asking questions within short order of my history professor lecturing on those topics. Gives me a chance to practice my test essays and also helps lock this stuff in my head.