The major political event that led to the dissolution of the Soviet Union was the August Coup of 1991. A failed coup attempt by hardline Communist Party members aimed to seize power from the reformist leader Mikhail Gorbachev, triggering widespread protests and resistance. The coup's failure accelerated the push for independence among various Soviet republics and undermined the legitimacy of the central government. Consequently, on December 26, 1991, the Soviet Union officially dissolved, leading to the emergence of several independent states and marking a significant shift in global politics.