As your empire grows .more of your acquired cities become so called failed states, i.e. obscene corruption kills all but about 1 shield and 1 commerce. The way to stop this is the we love the king day.
To have this do the following:
* Lots of luxuries with marketplace. 6 + is good
* Cathedrals & temples + Coliseums for the larger cities
* Free growth IE you need to have static growth or steady growth but not limited growth due to being at pop 6 without aqueduct or pop 12 without hospital.
* Short decisive Wars with democracy/republic.
* At least pop 6
When all of this occurs 2nd and successive turns of We love the King day lowers corruption. A failed state can be turned into a ‘core’ city after several turns increasing commerce which will enable you to recover other failed states.
So apply monetary aid to 1 city at a time. Applying a cathedral to multiple cities at the same time will reduce your ability to keep ‘feeding’ a failed state. After you set improvements to sustain a WLTKD , apply courthouses and police stations this will lower corruption and enable the recovery faster.
Religious/Communist/Despotic civs with conquered civs.
Corruption is also affected by nationality.
Nationality can be negated by the annihilating said civ and also engaging in several short sharp wars.
Using Religious ability change to Communist(preferably)/Despotic (if you aren’t already) then rush build Marketplaces/Cathedrals/Temples etc.
This has two benefits:
1. The cropped population will be of a different nationality. future growth will be of your nationality.
2. The Marketplaces/Cathedrals/Temples will eventually lead to a WLKD.
3. Culture generated by the Cathedrals/Temples will lead to quicker transformation of the indigenies.
4. If you are Religious make the quick switch back to your previous government and continue as before.
Religious is a useful trait when engaging in all of the above cheaper temples & cathedrals, quicker changes without undergoing 8 or so turns of dreaded anarchy.
Even if you are not religious you can still do the above strategy, make sure that enough cities are going to be cropped and changed in the above fashion otherwise you are probably better off using money.