Religion causes war. This is a matter of historical fact. Since time immemorial, men have fought each other in wars caused by religion. There are at least three instances by which religion causes war.
The first is when people try to compel other people to adopt their religion or religious perspectives. This comes from our innate tendency to want other people to subscribe to our beliefs. That desire can be accompanied with a strong zeal such that if others are impervious to our peaceful approach to convert them to our beliefs, we can even resort to violence to achieve that end. History is replete with such examples. One example was shown during the initial propagation of Islam when the Prophet Mohammad actually declared a holy war against the desert kingdoms and cities of Arabia. The purpose of the holy war was compel the infidel Arab people to embrace the new religion he had founded. This kind of religious conflict was also amply demonstrated during the Thirty Years’ War of the 1600s. Catholics and Protestants in Europe were locked in a long and devastating conflict that arose out of a desire of the warring religious and political leaders to force each other to accept their own interpretation of what Christianity should be.
The second instance when religion can cause war is when a nation of a particular religious conviction goes to war against another nation, not to convert it to their religion, but to simply eliminate them as people who are unfit to populate a certain geographical locality. It is nothing more but the expression of a bias against another group of people because they do not subscribe to the same faith or religion. This was the nature of the violence that erupted between the Old Testament Hebrew nation and their neighboring desert tribal nations such as the Canaanites, Edomites, and the Moabites. As narrated in the Bible, the Hebrews had to wage wars against these neighboring kingdoms, not so much to convert them to the Hebrew faith, but as an act of cleansing commanded by no less than their God who wanted to rid the Promised Land of people practicing other religions with allegiance to other gods such as Baal, who was a much hated deity in biblical history. This kind of war that partakes of the nature of a cleansing act had its modern version in the Serbian Christians’ attempt on ethnic cleansing to clear the newly created republic of Kosovo of its majority Muslim population so that the minority Christians of Kosovo could take over.
Finally, religion causes war because people of different religious convictions can easily distrust each other. In this instance, there is no attempt to either convert or eliminate each other. Two groups of people or nations go to war against each other because of they have a sense of misgivings for each other that can be traced to their difference in religious convictions. An example of this was the long conflict that had characterized the relationship of the Catholics and the Protestants in North Ireland. There had been no attempt to convert each other. Neither had each religious group attempted to eliminate each other from their geographical enclaves. It had been a war that was waged by two religious groups who had found it psychologically difficult to co-exist simply because they had different religious beliefs. It might be an oversimplification but in a sense, this is how we can characterize the strained relationship between the Christian and the Muslim worlds today. That strained relationship has found an outlet in what is currently termed the “war on terrorism” being being fought by the United States and its allies against a militant Islamic group called Al Qaeda.