|| 20 years cycle of regime change
No dynasty lasts forever. God brings a new one up, and throws the old one down. It's a cycle that the world had been going through since human history. 20 years isn't an exact number, just an average approximation.
|| Sins of a regime will come back to bite it
Come back to bite after that regime has lost power. As long as one is in power, God grants him freedom to do whatever he wishes. "What he wishes" was his test. Consequence of what he wished, is what he will get in return. No sin gets lost for ever.
|| Later regimes punish the older ones
And the one that will come after this one will punish this one. This is the cycle. And every regime is here for a reason. Therefore one regime's abuse won't cause it to fall prematurely before its time, it's here for the reason to punish the older abusers too. That task has to be fulfilled.
|| Was reading Gazzali's book
That book talks of a prophet who was so upset with the regime in power that he prayed to God for it to fall. God replied destiny was written thousands of years before you, including who will rule for what period. I won't change it because you can't be patient on his abuses. Why don't you rather migrate to another place if you can't be patient here?
|| Regime includes everyone in power
And it's not only the kings or governments. Everyone that leads a group, family, business or has authority on someone falls in this cycle. Therefore the best we can do is to be soft in our behavior. Everyone's time will end and he will find himself in a position that he despised. And find himself in the mercy of the weak ones who are now in power.