Also, stop immediatly bombing your enemies. stop even fighting. defend only, each day your civilian casualties go back. Change diplomatic relation to peace, may be some AI would accept it in several days. Build bunkers, recruit offices and hospitals for moral boost. Sell and buy ressources on market, so your popularity would growth a little bit. If you dont heve enough ressources for bunkers/ recruit offices and hospitals, sell every building in occupied provinces. Because you would lose it any way if those provinces revolt.

Next round dont be rusher. Look at your moral penalties before you get revolts in your home provinces...

There are many premissions for changing moral. Moral of one provinces is important for every neighbour-provinces. Borders to enemies have another penalties. and like i said some buildings have boost bonus.
And in cities could be moral saboteurs, also spies of other players.

You have a base morale level if a city is homeland, annexed, or occupied. Each lower than the previous. Factors that determine morale, are morale of surrounding provinces, civilian casualites caused, distance to capital, buildings present, and length of time occupied (please correct me folks if i missed some). So if the base morale of an annexed city is 50% and you just took it over and annexed it, it might be at 29% but say rising. It will say rising until it reaches 50% +- factors. So let's say you are at war with 3 countries -6, it is far from your capital -3, you have a hospital in it lvl 1 +1 , you have caused civ casualties -5, and finally the surrounding provinces (4 of them) are all at 25% morale -4. So you have a current morale of 29% which includes -18 and +1, for a total of -17. Since base morale is 50% (iirc) -17 is 33%. So your city will say rising until it reaches 33% and then become stable. If you add a bunker for a +3 it will go back to rising until it reaches 36, but then you are at war with 2 more countries (-4) it will say dropping until it reaches 32.

If you lose your capital -20, ALL cities take a -20 hit, which for many occupied put them in the risk area for uprisings. If an enemy is doing the rush attack and not building up morale in occupied cities, he probably is not keeping his homeland well guarded, send a few troops in to capture his capital. You won't hold it, in all likelihood, but at day change almost all of his occupied cities will go at risk of rogue, and likely a good chunk will go. Sure he takes his capital back the next day, but then he has to rebuild the capital (costly AND takes a day) so he loses even more cities and more than a few occupied provinces. Rush attack = over. It is a great way to slow down someone. Unless they are smart and leave forces in their capital.

I hope this helps, and as always if anyone sees a mistake I made, please correct me.