All war is made in the service of the ruling class, which attempts to usurp the only true authority - the authority of God (or the Creator or whatver you believe). Without allegiance to the ruling class, there is no war.

"I won't know the man who killed me
I won't know the men I kill
We end up on the same side
Ain't none of us doing God's will."

War is evil. The ruling class, by definition, is evil. Serving evil brings only more evil. There is only one ruler. The orders are to "love your neighbor as yourself". Any orders contrary to that are orders contrary to the only authority that exists. Those who issue those orders do so in the service of evil. Those who issue those orders do so in defiance of God. That never ends well.