Final answer:
The fall of the czar and rise of a socialist government in Russia in 1917 was directly triggered by the Bolsheviks' successful inroads, leading to the establishment of the USSR.
Explanation:
The event that directly triggered the fall of the czar and the emergence of a socialist provisional government in Russia in 1917 was:
- By late 1921, almost everywhere in the world, the great revolutionary wave stirred into motion by the First World War was ebbing away.
- Radical Russian socialists, known as Bolsheviks, made successful inroads with peasants and workers sick of war.
- October 1917, Lenin's Bolsheviks captured many of the major cities in Russia and instituted the Union of Soviet Socialists Republics (USSR).
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