Answering Allure's sub-question:
Any idea why these wars and insurgencies were less common during Soviet times as opposed to post-Soviet times? It seems there was nothing from the 1950s to late 1990s too
The period of 1950-1990 was the "cold war", and was characterised by a high level of militarisation. The security and integrity of the state and Party - and the satellite states such as Hungary - was the top priority.
In order to have a civil war two things are required: something to fight with (weapons), and something to fight for (organisation and ideology). Both of these were subject to incredibly heavy levels of control.
Military discipline was strong, so there was little leakage of weapons into private hands. In the post-Soviet period, many weapons were simply sold on the black market by the officers that were supposedly responsible for them. Also, since the USSR was extremely concerned about Western infiltration, and escaping dissidents, the borders were very tightly controlled making it difficult to infiltrate weapons. "The Iron Curtain" described the seemingly-impenetrable border between the West and the Soviet satellite states of Eastern Europe.
Ideological and informational control was also very strong. The opportunities for samizdat publication of political material were limited. Anyone attempting to organize a faction that might fight would be likely to be caught and severely punished.
Finally, to fight you must have an enemy, and two enemies readily existed: for those that believed the propaganda, they could unite against the West. For those that didn't, the biggest and most immediate omnipresent enemy was the state of the USSR itself. In both cases fighting one's immediate neighbors looks like less of a priority.
The risk of individual military units going rogue was mitigated by the usual tactic of empires: conscripts were split up and geographically distributed producing multi-ethnic units that had no particular loyalty to the region they were stationed in.