The best answer for this is a very simple yet emphatic NO. Religion is not what causes war. War is decidedly the result of sinful man’s intentions and darkness of heart. The concept of holy war is at best an oxymoron. From a Christian standpoint, there is no time when war is called for, unless it is to protect those who are being persecuted or endangered. There is simply no reason for a Christian to participate in war otherwise, nor is there reason for a government founded on Christian principles (like the US) to start one. Again, this is not to say that people of faith cannot participate in war, but that they are only to be involved when the war is justified by the presence of aggression on the part of the attacker.
There have been wars and conflicts where religion has taken the brunt of the blame (the Crusades and the current war by and on terrorism come to mind). However, even in these circumstances, it is not being perpetrated for godly reasons. The Crusades were a blight on the face of Christianity that resulted from the greed and avarice of many of the people involved, and the current terrorism being conducted by groups such as Al-Qaida is being perpetrated almost solely for political gain. The guise of religion is merely a mask foisted upon these heinous acts to give it some sense of legitimacy. Otherwise, unjust war goes against everything that a Christian is supposed to stand for.