"Why is there war?" I don't think there is ever a good reason or answer to that question. It is frigtening to think that human's are the only species that build weapons of mass destruction. While wars may be caused for the same reasons that they are started throughout the animal kingdom we are the only one's on this planet that have the power to wipe out an entire country. As you explained in your poem, war makes human life expendable, people are killed with out thought and in large numbers.
You have asked a hard question, "why is there war?" great poem.