WordNet
n. a campaign against entering or continuing a war
Wikipedia
An anti-war movement (also antiwar) is a social movement, usually in opposition to a particular nation's decision to start or carry on an armed conflict, unconditional of a maybe-existing just cause. The term can also refer to pacifism, which is the opposition to all use of military force during conflicts. Many activists distinguish between anti-war movements and peace movements. Anti-war activists work through protest and other grassroots means to attempt to pressure a government (or governments) to put an end to a particular war or conflict.
Usage examples of "anti-war movement".
Within three months, the anti-war movement would produce 100,000 protesters at the Lincoln Memorial.
Though Johnson was a write-in candidate who never came to New Hampshire to campaign, it was a big psychological victory for McCarthy and the anti-war movement.
Sam Brown, one of the most prominent leaders of the student anti-war movement, later got involved in Colorado politics and, when I was President, served the United States with the Organization for Security and Cooperation in Europe.