Uh, those despots survived because they had no opposition or rebels fighting back, champ.
You're doubling down. Terrific. Let me guess, public school?
Everyone of those men, excluding Kim Jong-Il, faced armed resistance to their tyranny at least once, many faced armed resistance several times or even continually.
Amin, Mugabe, Pol Pot & Duvalier (and several other Haitian dictators including Aristide) all put down insurrections that could only be described as civil wars.
Hussein's record, of course, speaks for itself as the only guy who (as far as we know) actually used WMD on "his people".
So yes, they did have "opposition or rebels fighting back".
Your welcome.