It is often the EXCUSE but not the reason, very different in my opinion. If tomorrow all religions disappeared man would still kill each other, still go to war, still take advantage of each other etc etc etc. I don't think more war would happen without religion, but it's certainly not the reason war happens. War is about power, money and land and many military leaders will motivate using religion. "Go risk your life and kill the other guy because our government needs more land and our bureacrats need more money and power!" That wouldn't motivate too many soldiers I don't think.