Worlds that belong to your empire will not blindly accept every one of your decisions or their consequences. If you fail to deliver needed raw materials, or worse, neglect to supply them with food, the people of the world will grow dissatisfied with your reign. If you consistently lose battles or fail to protect worlds in your empire, the empire as a whole will lose faith in your leadership.
The revolution index of a world is a measure of its dissatisfaction.
There are a couple of ways to lower the revolution index. Conquering an enemy will sometimes bring out patriotism in even the most rebellious worlds. And of course, time will allow worlds to forget about past wrongs.
If the dissatisfaction of a world grows, there is a chance that a rebellion will develop. If that occurs, people of all types will take up arms against imperial forces and attempt to return the planet to independent rule. Only imperial troops could stop this kind of opposition.
Effect of Troops on Revolution Index
Infantry legions affect the revolution index of the world on which they are stationed. The people of peaceful worlds do not generally enjoy having large numbers of troops around to remind them of war and conquest. Similarly, the judicious use of force on rebellious worlds can often dissipate tension and confrontation.
In general, worlds with a low revolution index will not like having many troops and their dissatisfaction with the empire will increase. On the other hand, worlds with a high revolution index will be controlled and subdued if there are enough troops on the world to put down insurgencies.
If the dissatisfaction of a world reaches a certain level, an armed rebellion is inevitable. Organized armies of rebels will attack imperial installations on the planet and try to gain control of the government. Usually, the only recourse for the emperor or empress at that point is to send in imperial troops to battle the insurgents.
The number of rebels that will fight is a function of the population, and the chance that a rebellion will succeed depends on the number of rebels and the number of troops. If the rebellion succeed, the world will become independent and all forces on the planet will revert to the control of the population. Even if the rebellion is defeated, the world will lose a number of infantry legions proportional to the number of rebel troops and the world will drop in efficiency by 5 to 15 points.