What, in your religious opinion, is a justification for war? What does your religion say about it, has it any prescribed 'rules' so to speak for when you should go to war, who can be killed, keeping slaves, who is eligible to fight &c.? What is your opinion? Are you warlike or a pacifist?
This is in debates so feel free to tell other posters why their reasons suck and yours are obviously better.
There are exceptions to my rule of thumb, most notably if God orders a war. However, one should note that even in such cases as God ordering a war, like with the Amelekites, there are plenty of human reasons for self defense.
The most common reason for instigating a war is to gain land, followed by gaining resources. I consider this immoral--it is not loving your neighbor as yourself. It is, at face value, incredibly horribly self serving at the expense of others. I would consider the deaths of others for these reasons to be a form of murder, even. Although honestly, something can be said for the fact that the poor shmoes actually doing the fighting are usually not there of their own free will, but have been forced or snookered into it. I would add to this category those who are using violence to spread an ideology such as communism. ISIS comes to mind, whose intent was to come into world domination and set up a worldwide caliphate in order to enslave people to Sharia Law and take away their free will choice to be other than Muslim.
It is perfectly moral, on the other hand, to defend again such vampires. Look, if you are living peacefully in your village, and barbarians ride over the hill, and their intent is to kill you, rape your wife and daughters, take your children as slaves, and take your land, it would actually be immoral of you NOT to fight to protect your family and the families of your neighbors. An example of this would be those who fought back against ISIS.