Gorbachev is a reformer but he is not a revolutionary.

Although Gorbachev is a reformer, he is not a revolutionary.

Inevitably, nNot only did he get pushbacks from vested interests and communist ideologues, but he also lost support from those who considered that he was moving too gradually.

Pushback is most often used in the singular form. The use of "inevitably" does not connect with the introduction of your statement.

For example, Yeltsin who supported Gorbachev in the first place graduallyitially. Gradually, Yeltsin lost his patience with Gorbachev’s slow pace: he. In response, Yeltsin quit the Communist Party and ran for the President of Russia as an independent candidate.

These sentences tend to be "run-on." Although I've included the subject Yeltsin in each sentence, it is easier to follow the argument being made.

At one point Yeltsin wanted, at one point, to work out another reformingation plan with Gorbachev, h. However, Gorbachev insisted that the reform must be carried out under the auspice of the Communist Party, which is a huge gap. This turned out to be a divide that they canould not bridge.

Reduction of comma use will improve the readability of your argument. As this event happened in the past, this would be a divide the two "could not" instead of present tense "cannot" bridge. The choice of "huge gap" for the "bridge" idiom could be better served by inserting "divide" instead.

The dramatic political maneuvering effectively resulted in the collapse of the Soviet Union, an astonishing denouement that iwas far from peaceful asthan it appeared to be.

The event happened in the past. Here the choice of "than" is to show a contrast.