Look into the nomadic peoples of arabia who gained power through trade. They aren't a perfect example because they did engage in violence but this could easily be adapted. Petra is also a very cool city you could look into, it was heavily fortified by its natural surroundings and therefore easily defensible in a way that minimizes harm.

I think your best option is a highly religious sect of nomadic traders for a number a reasons. The religion gives a source of their non-violent philosophy, trade gives them economic power with the least possible violence, and being nomadic makes it difficult to take this power from them through violent means.