Legitimacy is the quality that makes political authority feel entitled to obedience rather than merely capable of demanding it. Most people, most of the time, comply with authority without being directly coerced. Understanding why — and what withdraws that compliance — is the central problem of political order.
When the Soviet Union collapsed in 1991, the Red Army had nuclear weapons, tanks, and millions of soldiers. The state it served had none of those things destroyed. What collapsed was something else: the belief that it had the right to rule. Legitimacy cannot be seen, but its disappearance is the most consequential event in political life.