Most locales for most of history couldn't afford standing armies.

And not even from a financial standpoint -- there simply wasn't enough excess goods or food to have them out of the workforce.

Yes, that's true. A war machine requires surplus value. One reason why feudalism developed in Europe was for mounted warriors to be able to supply their warhorses. Facing constant violence, only super-appropriation of peasant surplus could give local lords and warriors enough resources to hold their own. And much of the success of many of the empires of history lies in their ability to requisition surplus value and use it to hire enough military labor. Rome could muster more soldiers than Carthage, for example.