Russian Civil War
Exclusion of Mensheviks and SRs

At the Fifth All–Russian Congress of Soviets of July 4, 1918, the Left Socialist-Revolutionaries had 352 delegates compared to 745 Bolsheviks out of 1132 total. The Left SRs raised disagreements on the suppression of rival parties, the death penalty, and mainly, the Treaty of Brest-Litovsk. The Bolsheviks excluded the Right SRs and Mensheviks from the government on 14 June for associating with counterrevolutionaries and seeking to "organize armed attacks against the workers and peasants" (though Mensheviks had not supported them), while the Left SRs advocated forming a government of all socialist parties. The Left SRs agreed with extrajudicial execution of political opponents to stop the counterrevolution, but opposed having the government legally pronouncing death sentences, an unusual position that is best understood within the context of the group's terrorist past. The Left SRs strongly opposed the Treaty of Brest-Litovsk and opposed Trotsky's insistence that no one try to attack German troops in Ukraine.

According to historian Marcel Liebman, Lenin's wartime measures such as banning opposition parties was prompted by the fact that several political parties either took up arms against the new Russian Soviet Federative Socialist Republic, or participated in sabotage, collaboration with the deposed Tsarists, or made assassination attempts against Lenin and other Bolshevik leaders. Liebman noted that opposition parties such as the Cadets and Mensheviks who were democratically elected to the Soviets in some areas, then proceeded to use their mandate to welcome in Tsarist and foreign capitalist military forces. In one incident in Baku, the British military, once invited in, proceeded to execute members of the Bolshevik Party who had peacefully stood down from the Soviet when they failed to win the elections. As a result, the Bolsheviks banned each opposition party when it turned against the Soviet government. In some cases, bans were lifted. This banning of parties did not have the same repressive character as later bans enforced under the Stalinist regime.
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