I don't see any biblical justification for this conclusion. Jesus Himself and James 1 say that corruption comes right from our own hearts. We don't need dark spiritual forces for us to be cruel or power-hungry. We are remiss to blame all of our violences on the dark side of the spiritual realm. They don't need to motivate us when our own hearts are so filled with sin.

Are most or all wars ultimately orchestrated by the dark side of the spiritual realm?

Even the United States involvement in WW2?

Does anyone know of material that makes a good case for this?