What ended Russia's involvement with WW1?

Answer 1

When the Bolshevik's seized power in Russia, they negotiated the Treaty of Brest-Litovsk with the Central Powers. In the treaty, Russia reneged on all previous treaty obligations to the "Triple Entente". The fairly high casualty count, heavy toll on the economy of supporting the war (including food shortages), military failures by Russian forces, deteriorating military morale, and offers of support to the Bolshevik rebels from the Germans weakened the Imperial Russian government to the point that first the Tsar was forced to abdicate and then the provisional government ceded control to the Bolsheviks. Even so, Russia was still embroiled in a civil war so fighting both the Central Powers and continuing the civil war was simply infeasible and the Bolsheviks found it very advantageous to sign the treaty and withdraw Russian forces from participation in WW I.