"Use of Weapons" is another in Iain M. Banks' series of "Culture" novels. For those not familiar with the series, the Culture is an interplanetary civilization in which disease, injury, age, material want, and even war are all things of the past. Citizens live their lives almost entirely as they choose, and information and aesthetically satisfying experience are valued above almost all else.
The permanent peace is made possible because the Culture is so heavily armed that only its ideals prevent it from obtaining any goal by force. In fact, the decision makers and the vast majority of ordinary citizens are so content, well-adjusted and just plain enlightened that they must recruit individuals who are maladjusted enough to be able to enforce their ideals. These individuals work for Special Circumstances, the part of the culture that deals with first contact (as in "Player of Games") foreign relations, and espionage.
Cheradenine Zakalwe is an operative of Special Circumstances. He is an immigrant to the Culture, and comes from a world steeped in conflict. As we come to understand, he is a man of action, inclined to solve problems with force. He is also intelligent enough to be a master tactician and (critically) needs ultimately to believe that he is a force for good in the world.
"Use of Weapons" reminds me of "All My Sins Remembered" by Joe Haldeman, in which a man is conditioned to be a deadly operative against his deeper ideals as a Buddhist. In both works, the larger conflict is for the main character to come to grips with his own identity.
Both "Use of Weapons" and the larger "Culture" series (particularly the original "State of the Art" novella) are highly recommended.