Can you explain what's the reason? You can say positive as well as negative reasons.
I think the most common reason for war is the urge to capture resources owned by another jurisdiction. For example, the USA frequently goes to war to secure access to energy resources.
That's quite strong allegations about the USA, yeah trump is a pain in the a**, but I don't think America goes to war for resources acquisition. There's world market to properly acquire resources you need for your country, and America participates well in that economy.
We're in the new era now, no such reason to support war specially if lives are at stake.