Pacifism is the opposition or resistance to war, militarism (including conscription and mandatory military service) or violence. Pacifists generally reject theories of Just War. The word pacifism was coined by the French peace campaigner Émile Arnaud and adopted by other peace activists at the tenth Universal Peace Congress in Glasgow in 1901. A related term is ahimsa (to do no harm), which is a core philosophy in Indian religions such as Hinduism, Buddhism, and Jainism. While modern connotations are recent, having been explicated since the 19th century, ancient references abound.

In modern times, interest was revived by Leo Tolstoy. In his late works, particularly in The Kingdom of God Is Within You. Mahatma Gandhi propounded the practice of steadfast nonviolent opposition which he called "satyagraha", instrumental in its role in the Indian Independence Movement. Its effectiveness served as inspiration to Martin Luther King Jr., James Lawson, Mary and Charles Beard, James Bevel, Thich Nhat Hanh, and many others in the civil rights movement.