should religion ever be used as a reason for war?

Most of us have all heard of 9/11 and the terrorist involved and some of us know about pearl harbor and the bombings from japan. Well I want to know why there religion tells them that if they go commit suicide and kill someone in the process that god will bless them in the after life? even though they know it is bad to kill they actually believe that their god will bless them for killing his people? please tell me what you think