Final answer:
The October Revolution of 1917 overthrew the tsarist regime and gave political power to the Bolshevik party in Russia.
Step-by-step explanation:
The major historical event that overthrew the tsarist regime and gave political power to the Bolshevik party in Russia was the October Revolution of 1917. It was a popularly supported revolution that led to the abdication of Tsar Nicholas II and the establishment of a socialist government by the Bolsheviks, led by Vladimir Lenin. After a period of civil war, the Bolshevik Party seized power and signed an armistice with Germany prior to the end of World War I.