People engage in war because they want to love or be loved. Although this may sound absurd at first, let's give it a closer look, because if we can understand the motivation for war then we might be able to redirect it.
The most fundamental human need is to be accepted, and the most fundamental fear is to be rejected. The old idea that survival comes first just doesn't hold up in the light of experience because it doesn't account for those who risk their lives for others, even strangers, and for those who commit suicide. And the fear of death is the fear of the ultimate rejection: by life itself.
Acceptance can be sought from oneself, one's environment (including people), or one's God, and many different strategies are used to ensure acceptance. If these strategies are pursued without fear, including fear-based anger, the result will be peace and cooperation. But as the fear of possible rejection increases, so does the tendency to seek acceptance by control or submission. Then the result is emotional repression, social suppression, and the use of violence to prove one's power or to make others accept oneself whether they want to or not.
In the case of war, the leaders who make the major decisions set standards to judge behavior by the "other side" as acceptable or unacceptable, motivated by their personal or group standards of self acceptance or acceptance from those around them. And those who obey the orders to march off to death and destruction are motivated by the desire to be accepted by doing "the right thing" or the fear of being rejected, and/or punished, for not doing it. What's so sad is that the fundamental intention is so good.
The "glory" of war lies in the experience of incredible bravery, intense companionship, demonstrations of skill, the overcoming of limitations, successfully protecting one's country or loved ones or companions, and the adulation for the winners. Yet, until we find a better way to satisfy the need for acceptance and the desire for real power, people will continue to go to war out of love.
Our great challenge, therefore, is not just to end war, but also to develop alternatives to war which still provide the benefits that only very intense experiences can generate, as well as satisfying the need for love.