To what extent was fall of the USSR in the years 1985-1990 due to the ending of the Brezhnev Doctrine?

There were several reasons behind the collapse of the USSR in the 1980s, many of which were intertwined. While the ending of the Brezhnev Doctrine, and the subsequent collapse of the Communist regimes in the Eastern bloc, contributed to this sudden downfall, there were perhaps more important factors. While the secessionist aspirations of the Baltic states were a big factor in the west of the Union, outside of those three states there was relatively little desire for independence from the Union, so it looked unlikely to collapse on its own. The actions of Boris Yeltsin in undermining the power of Gorbachev and launching his own Democratic Platform are not to be underestimated. The landslide victories that Yeltsin's party won in 1990 were a crucial step towards the dismantling of the USSR.However, the elections could never have happened without the actions of Gorbachev, who was undoubtedly the main factor behind the USSR's collapse. He was simply trying to do too much at once; with his programs of perestroika (economic restructuring) and glasnost (openness) the USSR was destabilised both politically and economically. To then attempt to repeal Article 6 (thus allowing multi-party elections) and also end the Brezhnev Doctrine was naive at best and outright foolish at worst. It left the USSR critically unstable at a time when events across the Eastern bloc showed people that there were alternatives to Communist rule; with no food in the shops and revelations of misrule arriving from all angles, the people were always going to welcome those alternatives with open arms.