> That is evidenced by the fact that the USSR had many, many more peaceful transfers of power than any dictatorship I can think of, and military/security service coups were always very unsuccessful. Ultimately this all comes from decentralization of power.
Saying the USSR had decentralized power is only true in a relative sense. What they actually had was a stable tripartite structure (security, military, party) where each 'leg' held a metaphorical gun to the head of the other two, but any two working in concert could take out the third. The party was the weakest of the three in terms of physical force but controlled promotions in the other two, the military had most of the big guns, and the security services watched and listened to everything and controlled information and movement. With a few extra checks and balances like political officers in the military, the whole thing was mostly stable even through transfers of political power, at the cost of periodic purges of the losers in power struggles (stable doesn't mean bloodless).
It's completely incorrect to say there was a tripartite structure - the party was in practice and in theory above the two other branches. The party routinely dictated to the security apparatus and the military, purged them, and so on, while the other two had so little power they saw the need to attempt coups which never came close to success.
Saying the USSR had decentralized power is only true in a relative sense. What they actually had was a stable tripartite structure (security, military, party) where each 'leg' held a metaphorical gun to the head of the other two, but any two working in concert could take out the third. The party was the weakest of the three in terms of physical force but controlled promotions in the other two, the military had most of the big guns, and the security services watched and listened to everything and controlled information and movement. With a few extra checks and balances like political officers in the military, the whole thing was mostly stable even through transfers of political power, at the cost of periodic purges of the losers in power struggles (stable doesn't mean bloodless).