A conscientious objector (CO) is a person who decides not to be a combatant in military forces under conscription.
There are many reasons for this decision such as nonviolent or religious beliefs, ethical and moral beliefs to not kill human beings or pacifism.
Countries treat COs in various ways. They have also been treated differently throughout history. COs have been arrested or had to pay a fine. Some countries punished them by killing them. After World War II, many Western countries created alternative non-military services (civil service) as alternative form for pacifists. Often there were commissions to decide if someone really did not want to do armed service because of his beliefs or because of fear of war.
European Court of Human Rights has judged the denial of COs is violation of freedom of religion and thought in 2013, as well European Union recognized the right of conscientious objector as one of fundamental rights.
Other websites
Alternative Service in the Second World War: Conscientious Objectors in Canada 1939-1945. Conscientious objectors in a volunteer army (Chicago Tribune article by Anthony DeBartolo) The National Registry for Conscientious Objection Conscience - the peace tax campaign "Thoughts for Young Men ..." a one-page leaflet Manifesto against conscription and the military system , with online signature, official website International Conscientious Objectors' Day (War Resisters' International) "Making a Choice: Conscientious Objection or Refusing to Register" (Resisters.info) The European Bureau for Conscientious Objection GI Rights Hotline The Central Committee for Conscientious Objectors (US) Mennonite Central Committee's listing of resources for CO's (US) Christadelphian Position And Experience Of Conscientious Objection War Politics by issue