A major argument of the book is that the imprecise, informal, community-building indebtedness of "human economies" is only replaced by mathematically precise, firmly enforced debts through the introduction of violence, usually state-sponsored violence in some form of military or police.

A second major argument of the book is that, contrary to standard accounts of the history of money, debt is probably the oldest means of trade, with cash and barter transactions being later developments.

Debt, the book argues, has typically retained its primacy, with cash and barter usually limited to situations of low trust involving strangers or those not considered credit-worthy.

https://en.wikipedia.org/wiki/Debt:_The_First_5000_Years#Synopsis

debt came first. social debt. debt to parents, debt to community. the first banks were temples. you pay your debt in installments to the temple as tithe to secure rights to work the land (rent/tenure). credit and debt systems worked within/among peoples, barter occurred between unrelated/low trust peoples. you don't trade the cobbler 6 flax for 2 shoes. he just makes you the shoes and you hook him up when you can. because you all know each other.

coinage and more recognizable banking came with expansion and conquest: payment of taxation in coinage, lending of coinage for finance in low trust societies / among low trust parties, a means to pay soldiers in places outside the framework of social debts, so they can secure their material needs to fight while abroad.

graeber's book is an incredible lens for viewing and understanding the origins of these systems outside the capitalist ideology of insisting upon its social relations as "natural."