Historical evidence It is certainly true that individual Christians and nations with a predominance of Christians have been in violent conflict with each other. In Continental Europe this is evident in the 17^th century thirty years war with its estimated 8 million fatalities. In the USA, the 18^th century Civil War would be another example with 800,000 deaths. And in the UK the war between the Roundheads and Cavaliers acted out the tension between a belief in hierarchical authority rooted in the Divine Right of the Monarch and one rooted in the authority of God-given individual conscience as communally interpreted. There were towards 200,000 deaths. More recently, there is the instance of the ‘Irish Troubles’ involving strife between Catholics and Protestants, where the death toll is around 3500.
Christian ‘just warriors’ This is not to say that the Christian religion is the sole cause of any of these conflicts, but there is no denying that it is a significant factor or that very large numbers of individual Christians were involved in fighting on the different sides. Christians have believed deeply that they were right not only to fight but to kill in order to achieve what they hoped would be a more just future than the present state of affairs. Exceptionally, in each of these conflicts there have been other Christians who have said categorically any such use of violence is wrong and contrary to the Christian gospel.
Many Christianities At the outset it must be acknowledged that the churches and individual Christians in Britain and in Germany were overwhelmingly convinced of the rightness of their nation’s declaration of war. It must also be recognised that there are many different versions of Christianity and of what it means to be a Christian. This is true with regard to the institutional families of Catholic, Orthodox and Protestant, within each of which there are many variants: http://www.philtar.ac.uk/encyclopedia/christ/index.html. It is also true in respect of individual congregations within them and most especially on the part of the individuals themselves.