Of unlawful warfare, what may be said of the other side?
Life feeds upon life.
Power is savage.
War is a savage writ. The last recourse before subjugation. Where law fails and tenacity of wills prevail.
The question should be, what is lawful warfare?
Or at what point do we call a circumstance war? When bullets fly or when law of domain becomes contested among bodies of power?
On one of the levels without ww2 and the cold war afterwards — there would never be the Internet and modern computers as we know them [1]
On a philosophical level — as long as there is a dualism, there is a constant battle and interplay between the sides. So war in one form or another is as inevitable as peace.
In a sense the whole life itself is a constant battle between good and evil, chaos and order, entropy and information [2]
On the surface — scarced resources, justice, religions are just silly stories that people create for themselves to sugarcoat and rationalize those (or other) deeply embeded into the reality drivers.
[1] https://www.amazon.com/gp/aw/d/1732265119/
[2] https://www.amazon.com/Into-Cool-Energy-Flow-Thermodynamics/... and other similar books
Also Jordan Peterson “maps of meaning” and any serious book on roots of religious myths and stories.