The primary factor leading to the dissolution of the Soviet Union in 1991 was the combination of economic stagnation, political reform, and nationalist movements within its republics. By the 1980s, the Soviet economy was struggling due to inefficiencies and a lack of innovation, compounded by the burden of military spending and an arms race with the West. Mikhail Gorbachev's policies of glasnost (openness) and perestroika (restructuring) aimed to reform the economy and political structures but inadvertently weakened the central authority and fueled demands for independence among various republics. By December 1991, the Soviet Union officially dissolved, leading to the emergence of independent republics and a significant shift in global politics.