Why did russia become so isolated from western europe in the middle ages?

With the weaknesses of its economic and political structures becoming acute, Mikhail Gorbachev embarked on major reforms, which led to the overthrow of the communist party and the breakup of the USSR, leaving Russia again on its own and marking the start of the history of post-Soviet Russia. The Russian Federation began in January 1992 as the legal successor to the USSR. Russia retained its nuclear arsenal but lost its superpower status.

Your answer will be a.