“The view that politics and religion should be kept entirely separate from one another is a relatively recent one in world history. The attempt, when it is made, is not undertaken because the two have absolutely nothing in common, but for precisely the opposite reason. Politics and religion not only overlap, but compete in their various functions… for better or worse, these two phenomena have shaped our history and culture…”
This overlap between politics and religion is nowhere more evident in Christian faith and practice than in a discussion of the Just War. Clausewitz is often referred when defining war, he said;
“war is not merely an act of policy but a true political instrument, a continuation of political intercourse, carried on with other means.”
For a Christian, this is no less true. It could be possible to say that the just war is a continuation of the relationship between politics and Christianity by other means. The just war is a war that has been legitimised according to a set of criteria laid down by Christian thinkers throughout the ages. But, how far have the criteria and the practice of just war been a reflection of the political and social conditions that Christians found themselves in? The purpose of this work is to examine the impact of contemporary conditions and how they affected Christian thinking on the just war. In a work of this size it is not possible to cover the whole of Christian history and thinking. The focus will be the period of time that saw the greatest activity in the development of the doctrine of just war in Christian thought; from the first centuries CE to the sixteenth century CE.
Beginning with the Early Church in the first centuries of Christianity the development of the doctrine of just war will be examined up until the time of Vitoria in the sixteenth century. It is undeniable that within this time Christian attitudes to war changed dramatically (if somewhat slowly). From the pacifist writings of the Early Church Fathers we arrive in the sixteenth century with a fully developed doctrine of just war with four distinct conditions; legitimate authority, just cause, right intention and just conduct. This development underwent many drafts and changes between the two extremes in the intervening years. During the course of this work the many drafts, and other strands of this doctrine- such as the participation of the clergy will be examined. This will be done in the light of the received tradition with which the individual writer worked, and the social and political conditions of the writer and of the Church as a whole. It has not been possible in a work of this length to evaluate every Christian writer who touched on the subject of war in this time frame. Rather, selections have been made with regard to those who, it could be argued, made major contributions to the doctrine of just war. It may be a surprise to some that people such as Martin Luther and Gratian are only briefly touched upon, this is not to dismiss their writings on war, rather, it is an assumption that their writings contributed little to the outline principles of the just war.
The Early Church Fathers, Ambrose, Augustine, Aquinas and Vitoria and their contributions to Christian thinking on war will form the basis of this work. The early Church Fathers will be examined to provide the background against which the later Christian writers were to write. Ambrose will be seen as the first major Christian writer to address the just war principles within the Christian tradition. Augustine is commonly regarded as the “fountainhead of tradition” and is the most quoted Christian writer on the subject of war. Thomas Aquinas is included in the chapter on Augustine and his influence on later medieval thought because his writings, it will be seen, were strongly influenced by Augustine. He is focussed on particularly because he is seen in some circles as the climax and epitome of the writers on the just war (see below p.29). Vitoria is credited with bringing the just war conditions to a close, and into the global, rather than European, society. Each one will be examined in turn to determine their reliance on received traditions, and any development they made themselves. If any developments were made (or not) it will be discussed if these developments (or non-developments) were as a consequence of contemporary social and political conditions, or for some other reason. In this way the development of the doctrine of just war will be examined in its historical context.
Alistair Kee Constantine versus Christ (SCM Press Ltd. 1982) p1
 Carl von Clausewitz On War p87.