The most accurate response regarding the main reason for the crumbling of the Soviet Union in the 1980s is:
The Soviet economy could not match U.S. military spending while meeting citizens’ demand for consumer goods.
While other factors, including Gorbachev's policies such as Glasnost and Perestroika, played significant roles in the political and social landscape, the economic strain was a fundamental issue that contributed to the dissolution of the Soviet Union.