Anathem by Neal Stephenson is a great treatment of this exact type of scenario. I'll let you read it yourself, rather than spoil the plot. Or you can read the tvtropes page on the novel for a cliff notes version.
More broadly, a warrior caste is defined by its ethics - why they fight, why they don't fight, who is and isn't an acceptable target, how much force is appropriate for a given situation.
Personally, I think it's important to distinguish between soldiers and warriors. A soldier follows orders from an external authority. A warrior is directed by internal code (bushido, chivalry, etc). A soldier fights when, where, and how he is told to fight. A warrior picks his own battles and methods.
The following Heinlein quote gives insight into the warrior mindset:
Duty is a debt you owe to yourself to fulfill obligations you have assumed voluntarily. Paying that debt can entail anything from years of patient work to instant willingness to die. Difficult it may be, but the reward is self-respect.
For a warrior, his/her duty is to stand between a group of people s/he has sworn to protect, and those who would do those people harm. The warrior has a vested personal interest in finding a non-violent resolution to a conflict, because that's usually the most efficient way to fulfil that duty.
Warriors try avoid fights not because they fear violence or death, or aren't capable of using it with ruthless efficiency, but because they the personal cost it imposes. To quote Dwight Eisenhower:
I hate war as only a soldier who has lived it can, only as one who has seen its brutality, its futility, its stupidity
Another consideration facing the warrior is that no matter how good s/he is, there's always a risk of being injured or killed, which would prevent them fulfilling their duty.
These factors combine to create the seeming paradox of the martial pacifist, creating an individual (or caste) who always strives to find the least-violent resolution to a conflict. They train and spar not for personal glory or one-upsmanship, but rather to improve their ability to fulfil their duty to others.
That doesn't mean that warriors aren't willing to stage pre-emptive attacks if that's what's needed. Nor do they believe in fighting fair: there are no rules once blades are out or bullets are flying. Push them too far and they're not just going to beat you, they're going to destroy you as quickly and efficiently as possible.
Another good resource for understanding this mindset is Marc MacYoung's blog No Nonsense Self Defense. He has a whole section for writers.