Someone or something that is peaceable tends to avoid conflict. A peaceable demonstration would most likely involve lots of protest banners instead of angry rioters.
A peaceable group of people finds non-violent ways to resolve disagreements — you could call such a group a peaceable society. This adjective is less common than the closely related peaceful. Both words come from the Old French pais, or "peace," and its Latin root pacem, "treaty of peace" or "absence of war."