The United States had the most active anti-war movement during World War II, with organizations such as the American Peace Mobilization and the Fellowship of Reconciliation leading the charge.

A.J. Muste founded the American Peace Mobilization in 1940, which became one of the most prominent anti-war organizations in the United States during World War II.

Dorothy Day, a Catholic pacifist and social activist, was a vocal opponent of World War II and used her newspaper, The Catholic Worker, to spread her anti-war message.

Vera Brittain founded the Peace Pledge Union in 1934, which became the largest anti-war organization in Britain during World War II.

The White Rose, Red Orchestra, and Edelweiss Pirates were all German anti-war organizations that operated during World War II, risking their lives to resist the Nazi regime.

Charles de Gaulle founded the Free French Forces in 1940, which became the main anti-war and resistance movement in France during World War II.

Mahatma Gandhi, the leader of the Indian independence movement, was a vocal opponent of World War II and advocated for nonviolent resistance to British rule.

Dwight Macdonald edited the anti-war magazine Politics from 1944 to 1949, which provided a platform for dissenting voices during World War II.

W.H. Auden wrote a series of anti-war poems during World War II, including 'September 1, 1939' and 'The Shield of Achilles'.

Casablanca, released in 1943, is an American anti-war film set during World War II that explores the moral dilemmas faced by individuals in wartime.

Dorothy Thompson, an American journalist and radio commentator, was a vocal opponent of World War II and criticized the Roosevelt administration's foreign policy.

Ammon Hennacy founded the Catholic Worker Movement in 1933, which became a prominent anti-war and pacifist organization during World War II.

John Dewey, an American philosopher and educator, was a vocal opponent of World War II and argued for the importance of nonviolent conflict resolution.

Norman Thomas, a prominent American socialist and pacifist, led the Socialist Party of America, which opposed World War II and advocated for a negotiated peace.

Edward Hopper, an American realist painter, created a series of anti-war paintings during World War II, including 'Nighthawks' and 'Gas'.