Short answers, pulled from the story.
A small party of British troops landed in Murmansk on the 4th of March 1918. This event occurred the day after the Treaty of Brest-Litovsk ended hostilities between Germany and Bolshevik Russia.
Japanese forces deployed over 70,000 soldiers by mid-1918 making them the largest single contingent present throughout Siberia. American forces included roughly 13,000 soldiers split between Arkhangelsk and Vladivostok commands while Canadian contributions reached approximately 4,192 men stationed primarily in Siberia with additional groups in Arkhangelsk.
The initial goal was not to overthrow Lenin but to secure munitions and supply depots from falling into German hands. Allied powers feared that vast quantities of war material stored in Russian ports would be seized by the Central Powers following the Treaty of Brest-Litovsk.
Last British troops left Baku on the 24th of August following similar pressures from regional instability. Murmansk was abandoned on the 12th of October marking the end of active combat operations there.
Japanese military remained stationed in Maritime Provinces until 1922 and northern Sakhalin until 1925. The Soviet, Japanese Basic Convention signed in Beijing formalized Japan's agreement to withdraw its remaining forces.