august thalheimer berlin bolshevik clara zetkin comintern communist party of germany communist revolution franz mehring freikorps friedrich ebert general strike german language germany imperialism independent social democratic party of germany julian marchlewski kaiser karl liebknecht leo jogiches luxemburgism marxism paul levi philipp scheidemann republic revolutionary roman republic rosa luxemburg russia russian empire social democratic party of germany spartacus weimar republic wilhelm liebknecht wilhelm pieck world war i