Hunger

That is usually the line when society will start moving towards revolution and change.

Get a little hungry? ... people start getting angry

Get more hungry? ... people start protesting

Face starvation? .... people no longer have anything to lose and violent revolution becomes the only option. Why sit around waiting to die when you could just try fighting with a remote possibility of winning when your option is certain death?

This is also the reason why the whole western world does their very best to keep us poor but not so poor that we become hungry. As long as we're fed, can afford some food or have access to food, we'll let the powers that be do whatever they like.