> Money originated as a way for kings to pay troops, who operated outside these village economies.

That’s one theory, and it’s not even the one Graeber preferred. According to him (and supporting evidence) money originated as a way to “keep score” of debts.

The question of the origin of money is an interesting one, but that will be probably be unsolvable, since some of the alternative theories (like barter) would leave little to no evidence.