Why exactly did the Soviet Union collapse?

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Whenever MSM touches on the subject, virtually no real explanation is given as to the precise causes of the Soviet collapse.
Sometimes they do mention a bunch of factors, such as nationalism and economic malaise, but without properly addressing how these came to be or how they became severe enough to destroy what was still a fairly young superpower.

So what happened exactly? And was it more attributable to malice, incompetence, or factors beyond human control?