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.
Substantial anti-war sentiment developed in America during the period roughly falling between the end of the War of 1812 and the commencement of the Civil War, or what is called the antebellum era. (A similar movement developed in England during the same period.) The movement reflected both strict pacifist and more moderate non-interventionist positions. Many prominent intellectuals of the time, including Ralph Waldo Emerson, Henry David Thoreau (see Civil Disobedience) and William Ellery Channing contributed literary works against war. Other names associated with the movement include William Ladd, Noah Worcester, Thomas Cogswell Upham and Asa Mahan. Many peace societies were formed throughout the United States, the most prominent of which being the American Peace Society. Numerous periodicals (e.g., The Advocate of Peace)) and books were also produced. The Book of Peace, an anthology produced by the American Peace Society in 1845, must surely rank as one of the most remarkable works of anti-war literature ever produced.