The cause of decline was the policy initiated by Mikhail Gorbachev in 1985 called Glasnost. It was a policy of openness and transparency. Glasnost which can mean Publicity encourage a dissemination of information. It was used by Gorbachev to reduce corruption amongst the communist leaders of the Soviet government. However this backfired as the public learned of long standing political cover ups revealing past and recent social and health failures of the USSR. This further eroded support for the regime. Secondly is the Stagnant economy. The Soviet Union had grown to a size large enough to a point where it became cumbersome to continue state planning. It became too large to manage thus it resulted in failed economic polices.
The political reforms was that the USSR officially ceased to exit on 31 December 1991. It change a worlds political balance. Tension between the US and USSR arose. During this time NATO tried to limit the spread of communism. In 1956 the Soviet invaded Hungary, this caused more tension and decline in Hungary power. However for the Economic reforms, the Soviet Union grown to a size large enough to the point where it cannot be handle. The massive Soviet union economy became too large to manage by planners. This resulted in failed economic policies.