No matter how compelling the structural factors driving history, individual personality and human agency remain relevant.

That still leaves the question, “Why 1989? Why under this leader?” To some extent, Gorbachev was an accident of history. In the early 1980s, three old Soviet leaders died, one soon after the other. It was not until 1985 that the younger generation, the people who had come up under Khrushchev, the so-called generation of 1956, had their chance. But if the members of the Communist Party Politburo had chosen one of Gorbachev’s hard-line competitors in 1985, it is quite plausible that the declining Soviet Union could have held on for another decade. It did not have to collapse so quickly. Gorbachev’s personality explains much of the timing.

Source: Russia in Global Affairs.