War! What is it good for? Absolutely depends on whom you ask. Scholar Michael Ward reads Prince Caspian as a story centered on war and martial law. It's all about the need to fight rather than "allowing aggressors to have their way." To balance this, he argues that Lewis included chivalry to "[impose] restraints on the practice of war so as to avoid unnecessary (that is cruel) violence" (source). Then again, David Holbrook reads a novel where "the trouble is that excited delight in violence is combined with a tone of endorsing it as all jolly good fun, and then endorsed by [a] solemn didactic message, urging that this is the way to the Kingdom of Heaven" (source). Ultimately, we'll say this: war is undeniably an important theme in Prince Caspian, but whether or not that's a positive thing will depend on the reader.
Caspian's war with the Telmarines is an example of a holy war. Its main goal is to change the religious standard of Narnia.
Alternatively, we could look at Caspian's camp as a group of environmental terrorists done Narnia-style.