What is responsible for wars is the fruit of the tree (Genesis 3:5). This is the notion that one can be the lord of their own life. That they should be able to decide good and evil for their self. Sort of a god of "self" doing what is right in their own eyes, and this leads to a might makes right philosophy among groups of "self" gods who come to agreement.
One person, or group (like gangs), or one tribe, community or nation (religious or not) who tries to lord it over others is always the cause of conflict. When a husband or wife insists on their own way that is tragic and when both want to be lord of the relationship this leads to discord and divorce...when one political party insists on only its way this leads to deadlock and fighting in a nations capital, when one nation tries to impose its way on another there is no doubt pain and suffering ensue and oh yes war.
So though I could easily demonstrate that ONE atheist like Stalin has systematically eliminated more people (many of his own countrymen) than all religious wars combined, the problem is "self" lordship!
Paganism, Political institutions, Atheism, Religions, and so on???? These are just vehicles through which this need to "self" dominate is carried...only a relationship with the true LORD, or at the very least, loving others as they themselves would want to be loved, is the only remedy...until then you are part of the problem not the solution.
ISIS is pure evil because of what it does and how it acts, not because it is Muslim....they steal, kill, torture, rape, etc., it does not matter what name or cause they do it in...and like any other cancer (a group of self willed cells imposing their way upon all others) they must be cut out or irradiated and eliminated to save the whole body (humankind). As once said evil only exists as long as good men do nothing.
AS individuals become "other" oriented and concerned, the world heals (one soul at a time). We can not force this by arms, and cannot legislate it by laws, it is a change in the nature of a man's will, and sadly nature can never do this, because nature knows only animalism (like all beasts of the field). Survival of the fittest defines the most powerful and fearful as the fittest (eventually it is interpreted as might making right) and this is wrongly interpreted as their genetic right, and thus history only gets interpreted by the victor and the suffering continues.
Paul