The virtual collapse of the old regime during the latter part of World War I helped to motivate the Mezhraiontsy to make amends with their Bolshevik rivals, headed by Lenin, and early in 1917 Trotsky returned from exile in New York City by way of Canada to join forces as a member of the Bolshevik party's governing Central Committee. Trotsky was instrumental in laying the groundwork for the 7 November 1917 seizure of power from the Russian Provisional Government headed by Alexander Kerensky, taking over as head of the Petrograd Soviet early in October and building that institution's Military-Revolutionary Committee into a revolutionary fighting force.