Frey said:
2) Rebellions are the polar opposite of the Golden Age. In Civ 5, as long as you have more than zero Happiness, you are on your way to a Golden Age. Civ 6 should have another counter running alongside the Golden Age counter, known as the Rebellion counter. Negative amounts of Happiness contribute to the Rebellion similarly to how positive amounts of Happiness contribute to the Golden Age counter. If your Happiness stays in the red and reaches a certain threshold on the Rebellion counter, then your civilization will enter a Rebellion phase lasting a number of turns. No Wonders may be constructed during a Rebellion and your civilization's Culture output is decreased. Other civs will have a easier time conducting espionage operations in your cities during a period of Rebellion. Stationed military units may be used to put down dissenters, but this comes at the cost of reducing the city's population.
You do know what happens in Civ5 if you have sufficient negative happiness, right?