Thats not true. (It’s a common libertarian trope.)
We have MADE conflict increasingly costly. However, predation is incredibly rewarding and every expansionary empire in history is evidence of it. Hell, american ascendence, and american quality of life is perhaps the best example in history. I can’t think of any condition in history where expansionary conquest wasn’t the most profitable endeavor possible.
I think we can say that SYMMETRIC conflict is costly, but ASYMMETRIC conflict is extraordinarily rewarding – hence the eternal arms race from the dawn of time.
Conquest and Rule are THE MOST PROFITABLE INDUSTRIES ever invented by man.
And we invented it.