The belief and, consequently, conduct of those who believe that war and the employment of organized armed force are unjustifiable. Until the 20th century this was a view held only by such minority Christian groups as the Quakers and the Plymouth Brethren. The word 'pacifism' first came into use at the beginning of the 20th century to describe movements advocating the settlement of disputes by arbitration and the reduction of armaments. Efforts to influence national policy in favour of the unilateral renunciation of war have continued in the face of the objection that a nation, which adopted such a policy, would be more likely to encourage than discourage aggressive action. From the time of World War I, the word has also been used to describe the refusal of individuals, on grounds of conscience, to undertake military service, whatever the consequences to themselves. States have varied a great deal in their treatment of such a refusal.

See pacifism and nonviolence for a wider discussion