Unhappiness penalty: When happiness drops to 13-15% in regions, the game sharply lowers the overall tax rate. Instead of the 20% tax (for 100% happiness), you are likely to receive only 7-9%.
How it works: Residents in the regions are furious—they demand roads, parks, and communications. Until their needs are met, the overall efficiency of tax collection at the Town Hall drops, even if everything is perfect in the Capital itself (99%).
What to do to raise income:
Provide services to the regions: Put basic services (water, light, sewage, garbage) there. A 13% happiness means they don't have something vital.
Demolish residential areas in the regions: If you do not have the resources to maintain them, simply remove empty/abandoned houses in the regions. The population will decrease, but average happiness will instantly soar to 99–100%, and taxes in the Capital will return to normal.
Roads: Check if there are any red congestion in the regions. It's the cheapest way to boost happiness by a few percent.
Once you raise happiness in the regions to at least 90%, your daily taxes at the Town Hall will increase 2-2.5 times.