And some guerrilla movements are simply the expression of a group of people who wish to seize power for their own glory and profit. It is of course not always easy to distinguish the motivations. Furthermore, the people against whom the guerrillas are fighting regularly ascribe motivations to the guerrillas that are different from those the guerrillas claim publicly for themselves. One of the characteristics of a state in the modern world-system is that it claims the exclusive legitimate right to the use of violence within its frontiers. For any state, guerrillas are illegitimate, and indeed immoral.
States seek to suppress guerrilla forces.
The main problem of guerrilla forces is how to survive against the efforts of the state to suppress them. First of all, they need some sort of popular support. The list of guerrilla movements that have failed because they couldn't muster some active support from the populations in their zone is long indeed. One famous example is the failure of Che Guevara to establish a guerrilla base in Bolivia, leading to his death and the elimination of his group. But popular support is not enough.