The increased Soviet defense spending and the war in Afghanistan combined with a moribund economy forced the Soviets to make difficult decisions. Mikhail Gorbachev attempted to reform the Soviet economy, but discovered that you cannot give people a little bit of freedom and starting in 1989 the Warsaw Pact nation’s spurned communism in a series of peaceful revolutions. Starting in 1987 with the signing of the IRBM treaty with Washington the Soviets tempered their positions in the face of continued US confrontation. In 1989, the Soviets acknowledged they could not win in Afghanistan and withdrew their military from the country. In 1991, the Soviet regime collapsed due to the dual pressure of political reformists and the terrible economy occasioned by the attempt to match US defense expenditures.
Ultimately, the Afghan invasion and the renewed confrontation with the west it caused led to the fall of communism in not only Russia but throughout Europe. The communist regime was unable to compete with the economic power of the west and in fact became increasingly dependent on western loans in order to stay in power. Communism proved itself a failed model and the renewed cold war strained the communist system more than it could take. Communism was probably doomed anyway; the Afghan invasion and its consequences only sped up the collaps