An uprising will happen during mission 10: 'Independence Day', even if your overall happiness is way over 50%. You're required to build a radio station. This ratio station will be occupied by rebel agents, have your army deal with it. Later, you have to switch your Ministry to People's Commitee and gain 130 Revolutionists. A 'fake' uprising will happen right after you've gathered them. After a few seconds Penultimo will inform you that it is a real uprising. You will win the campaign mission if you suppress this uprising, it will also unlock the achievement.