The Just war theory maintains that war may be justified if fought only in certain circumstances, and only if certain restrictions are applied to the way in which war is fought. The theory that was first propounded by St Augustine of Hippo and St Ambrose of Milan ( 4th and 5th centuries AD) attempts to clarify two fundamental questions: ‘when is it right to fight?’ and ‘How should war be fought?’. Whereas Pacifists are people mainly Christians who reject the use of violence and the deliberate killing of civilians but claims that peace is intrinsically good and ought to be upheld either as a duty and that war can never be justifiable. However, Realists agree that, due to the nature of humans, force is a necessary action to be used to maintain a just and ordered society. Therefore, since the Second World War, people have turned their attention to Just War again establishing rules that can serve as guidelines to a just war- the Hague and Geneva conventions.
Many Christians had taken the view that war may be justifiable under certain circumstances, and only if fought observing certain rules of conduct. Wars against the Muslim control of Jerusalem in the 11th-13th centuries were sometimes seen as holy wars which were popularly regarded as Crusades. Some philosophers based their justifications on the stories in the Bible. For example, St Paul in Romans 13:4 wrote that rulers are servants of God ‘…for he is the minister of God, a revenger to execute wrath upon him that doeth evil’. In the 13th century, Thomas Aquinas gave an outline (the first three criteria of a just war) on the Justification of war and the kinds of acts that are allowed in a war in Summa Theologica. His ideas became the model of later scholars such as Franciso Suarez and Francisco de Vitoria.
The first three conditions necessary for a just war were listed by Aquinas which included right authority, just cause and just intention. These and