An anti-war stance obviously brings up the question “how can Christians be so tolerant in participating in it”. I found this interesting…
In the early Christian Church followers of the Christ refused to take up arms.
In as much as they [Jesus’ teachings] ruled out as illicit all use of violence and injury against others, clearly implied [was] the illegitimacy of participation in war… The early Christians took Jesus at his word, and understood his inculcations of gentleness and non-resistance in their literal sense. They closely identified their religion with peace; they strongly condemned war for the bloodshed which it involved.
—The Early Christian Attitude to War.
After the Roman Empire officially embraced Christianity, the Just War theory was developed in order to reconcile warfare with Christian belief. After Theodosius I made Christianity an official religion of the Empire, this position slowly developed into the official position of the Western Church. In the 11th century, there was a further shift of opinion in the Latin-Christian tradition with the crusades, strengthening the idea and acceptability of Holy War. Objectors became a minority. Some theologians see the loss of a pacifist position as a great failing of the Church; see Constantinian shift and Christian pacifism. Mountains of individual debt, applied judiciously seemed to facilitate this transition.