True.. but in a superinflate economy state, soldiers will refuse to take that currency since it will worth nothing, and looking for something else, like a better and foreign one, or commodity or land, or whatever they can still from the place they are invading.. they will be soldier until the incentives to be one are greater then losing their life.

So if for absurd the last currency to stand will be dollar, when they will notice the currency they are paied by is becoming worthless, they will start to completely lose trust in the ones issuing them and in the currency itself. That's how Rome failed, expanding its territories to have more land to give to it's army and the taxing that out, but the expansion came with costs that were higher then doing expansion war itself and maintaining stability of these new lands.