What were the major factors that led to the dissolution of the Soviet Union and the collapse of the Eastern Bloc?

There are disputes over this issue, particularly over
whether Ronald Reagan or Mikhail Gorbachev was more responsible for the fall of
communism.  I would argue that Reagan and Gorbachev's actions were proximate causes. 
The real root cause of this collapse was the fact that the Soviet system could not
provide for the material or political desires of its
citizenry.

The Soviet system was very inefficient.  It was
not able to produce enough goods and services to give its people a good standard of
living.  At the same time, the political system was very repressive.  It did not afford
people the ability to have their voices and their frustrations heard in any meaningful
way.  This meant that a great deal of dissatisfaction had built up in the populace of
Eastern Europe by the 1980s.  When Gorbachev instituted his reforms and/or when Reagan
put more pressure on the Soviets by ratcheting up the arms race, the communist system
collapsed.