In recent decades the struggle for peace has increasingly taken on an antiwar character. Waves of disarmament activism have alternated with massive antiwar campaigns in an era of almost permanent peace mobilization. Movements against unpopular wars have multiplied and reached unprecedented scale, most dramatically in response to US aggression in Vietnam and Iraq. These movements are a reaction to the process of militarization that crystallized in the cold war era. As peace advocates had warned, the permanent mobilization for war that emerged in the wake of World War II reinforced the predisposition of political leaders to use military force and created greater institutional capacities to intervene in the affairs of other countries. Militarist tendencies developed in a number of major powers, but US military interventionism was most frequent and had the greatest global impact. When these interventions were particularly costly and egregious, as in Vietnam and Iraq, antiwar mobilizations reached massive scale and acted to constrain warmaking options. This is a new phenomenon in history, one that has made the peace movement a more important and controversial political actor. Antiwar protest, actual or prospective, has become a consideration in the calculations of government leaders and has started to emerge as a potential influence in the global politics of peace.

The scale of antiwar protest is largely determined by the nature of the particular conflict in question. The wars against Vietnam and Iraq were so obviously unjust that they prompted massive opposition.