Ehh... I haven't actually played that far in BNW, I played too many hours and am burned out. But apparantly Epic speed had my going on, go figure.
Anyway I took Freedom ideology, only Germany had that. I was just overtaken by Russia in Science but was still in charge of the game I felt.
Then suddenly I went from + happiness to 32 unhappiness. I am not even sure I noticed at first, it was just there. Order was the dominant ideology and it has something to do with that. I bought up a merchant CS and was bringing unhappiness down. Then my middle city on the map revolted and became English.
What can you do to combat or prevent that massive unhappiness?
Before it gets to that stage? Produce a lot more culture and tourism.
Once you're in that position? Change ideologies.