Happiness when you have many cities and want to keep expanding is a tough stat to maintain in Civilization V. Here are some things that will help you keep the happiness level of your Civilization in the positives. Remember, it's best to have a clear plan on getting these resources, buildings or social policies as early as possible, because taking over or building a new city generates a lot of unhappiness. So make sure you can build some of these buildings before you expand your empire too much.
Unique / Luxury Resources give +5 happiness each. Try to scout early and find these, they are very valuable not only for the added happiness, but for trading with other civs for their own unique resources as well.
Buildings that increase happiness:
Circus (if you have Iron and/or Horses nearby)
Colosseum
Courthouse (eliminates unhappiness from occupying a city)
Theatre
Stadium
The Burial Tomb, a unique building for the Egyptian civilization increases happiness as well.
Wonders that increase happiness:
Eiffel Tower
Notre Dame
The Hanging Gardens
Social Policies that increase happiness:
Legalism (Tradition)
Meritocracy (Liberty)
Military Caste (Honor)
Piety
Theocracy (Piety)
Cultural Diplomacy (Patronage)
Protectionism (Commerce)
Humanism (Rationalism)
Freedom
Planned Economy (Order)
Police State (Autocracy)
Brave New World Update!
With the Brave New World civilization 5 DLC, there are new ways of increasing happiness. One example is the new Idelogies. Here are all the different bonuses you can get: (From Order, Freedom and Autocracy:
- Universal Healthcare: +2 Local Happiness from every National Wonder.
- Socialist Realism: +2 Local Happiness from Monuments. Build Monuments in half the usual time.
- Young Pioneers: +1 local Happiness from every Workshop, Factory, and Solar/Nuclear/Hydro Plant.
- Academy of Sciences: +1 Local Happiness from every University, Observatory, Public School, and Research Lab.
- Capitalism: +1 Local Happiness from every Mint, Bank, and Stock Exchange.
- Urbanization: +1 Local Happiness from every Granary, Water Mill, Aqueduct, and Hospital.
- Universal Suffrage: Specialists in Cities produced half the normal amount of Unhappiness. Golden Ages are 50% longer.
- Fortified Borders: +2 Local Happiness from every Walls, Castle, Arsenal and Military Base.
- Universal Healthcare: +2 Local Happiness from every National Wonder.
- Militarism: +2 Local Happiness from every Barracks, Armory and Military Academy.
- Police State: +3 Local Happiness from every Courthouse. Build Courthouses in half the usual time.