One who opposes participation in military service, on the basis of religious, philosophical, or political belief. A feature of Western society since the beginning of the Christian era, conscientious objection developed as a doctrine of the Mennonites (16th century), the Society of Friends (17th century), and others. Exemptions may be unconditional, conditioned on alternative civilian service, or limited to combat duty. Those who refuse conscription may face imprisonment. Philosophical or political reasons are acceptable grounds for exemption in many European countries, but the U.S. recognizes only membership in a religious group that endorses pacifism.