Sid Meier's Civilization V: Brave New World/Ideologies

The late 3 Social Policy branches have been heavily revamped in Brave New World, now expanded into ideologies. Ideologies are composed of tenets that function very similarly to Social Policies in that Culture is used to adopt either of them. However, there are a lot more tenets in an Ideology than there are in a Social Policy branch, and you get a bit more freedom with the order you adopt them in.

A civilization can and must adopt an Ideology once they have built three Factories or entered the Modern Era, whichever comes first. The first civilization to adopt a particular Ideology gets 2 free tenets, while the second civilization to adopt a previously taken Ideology will only get 1 free tenet. Later adopters get nothing at all. Like the Social Policies they were based off of from the core game, Ideologies are mutually exclusive and strongly affects diplomatic relations. Since AI civilizations will often prioritize Ideologies that still have free tenets, it's practically guaranteed for Ideologies to clash, radically changing the world stage.

Ideological pressure
Civilizations with differing Ideologies exert ideological pressure on each other, which affects your Public Opinion. Public Opinion depends on the Culture and Tourism output of both competing civilizations. Tourism is your way to "attack" other civilizations with your influence, reducing their Public Opinion. Culture generation negates Tourism from enemies, protecting your empire from enemy Ideologies.

Once Public Opinion drops from "Content" to "Dissidents" and below, it will start creating Unhappiness in your empire. Once you reach "Civil Resistance" and then "Revolutionary Wave", your cities will start spawning Rebels which attack your cities and infrastructure. After your Unhappiness exceeds 20, entire cities will revolt and join the empires of influential civs instead.

If raising Culture to defend against enemy Tourism or raising Happiness to counter dissent isn't enough, a last resort is to switch Ideologies to the one your citizens prefer. Doing so will likely raise your Public Opinion back up, but it comes with some serious drawbacks. Switching your Ideology causes you to lose the effects of any tenet you've adopted from your previous ideology. An empire switching Ideologies also undergoes a turn of anarchy, during which nothing will be produced.