Pacifism was the ethical position that violence and war are immoral. Strict pacifists refrained from all forms of violence, while restricted pacifists made some exceptions, for example, in cases of self-defense.
In the late 1930s of an alternate timeline created by Leonard McCoy's escape through the Guardian of Forever, Edith Keeler lead a pacifist movement that delayed the United States' entry into World War II, thereby giving Germany the time they needed to develop the atomic bomb first and win the war. (TOS: "The City on the Edge of Forever")
- Vulcans (insofar as they follow the teachings of Surak)