The term anti-war sometimes refers to pacifism, i.e., opposition to all use of military force during conflicts, but most often is used in the context of opposing one particular nation's decision to wage war. Many activists distinguish between anti-war movements and peace movements. Anti-war activists believe that most wars have an aggressor and that their movement works to ensure that the aggressor (whose goals they see as selfish) ends their war.

Use of the term can cause confusion:

* is an "anti-war activist" equally opposed to both side's military campaigns or are they choosing one side in particular?

* likewise, does against the war indicate a pacifist objection, or a preference for the victory of one side?

Some uses of anti-war suggest that only one side is waging a particular war, implying that if that party were to withdraw or surrender, the war would cease to exist. Much rhetoric about the role of the United States in the Vietnam War employed this usage, as did that of demonstrators in Russia demanding an end to that nation's involvement in the First World War.

Anti-war movements and pacifist movements are related, but are not one and the same, although members of anti-war campaigns often marshall pacifistic imagery and arguments. Pacifism is the belief that conflict is never acceptable, and that society should not be structured to maintain a stance of readiness to fight in a conflict (See disarmament). While pacifists oppose all war, "anti-war" activists may seek only to get one side to withdraw.

Source : http://en.wikipedia.org