What were the main factors responsible for the disintegration of the Soviet Union?
Generally, the capability of the USSR to maintain its internal and external economic structure eventually failed, and the political structure followed. Factors included the dissatisfaction of its citizens, nationalist movements in Eastern Europe and Asia, and an unworkable, inflexible bureaucracy.
The Soviet's tightly controlled economy was not able to compete with the free-market economy of the US and its allies. In almost every area of competition - excepting only nuclear armaments - the Soviet system fell behind. One example of this can be found in the production of Soviet steel. Around and after WWII, the Soviet system was behind the US in steel production. Since they used a command economy, this was a factor that had to be settled not via supply and demand but rather through the Soviet government's use of limited resources and time (e.g. currency and time). By the 1990s, Soviet steel production surpassed that of the US. Unfortunately for the Soviets, by this time there was a plethora of steel traded on the open markets. So while they did indeed begin to produce more steel than the US, it was more expensive for them to produce steel domestically than it was for the US to import it. This left the US with resources to spend on other "projects" - such as computer technology. This phenomenon was to repeat itself in a variety of other areas as well.
The move away from nuclear arms to conventional arms was one that the USSR was ill-prepared to exploit, although Russian scientists were among the best in the world. When Ronald Reagan became President in 1981, he embarked on an ambitious expansion of the armed forces, requiring the Soviets to expand their own cumbersome military apparatus. When the Russian and Soviets economies fell on hard times, they could no longer afford to control their satellite countries in Asia and Eastern Europe.
Communism vs. Religion
Russia fell primarily because the Great God of Abraham Isaac and Jacob caused it to fall. For more than 60 years Godless communism had enslaved and murdered people all over the globe and espoused that the state was God. Afghanistan was the first chink in the mighty Soviet armor. Then the other "stans" broke away. All those soviet vassal states with great numbers of Muslims broke away, and the communists lost control of their empire. Mainly God allowed thousands of Jews to return to return to Israel from Russia. The great red bully of the world was shaken to the core and split up when God decided that enough was enough!