Even if the peace system moduled 'political realism' in which the strong do what they can, it seems a bit exessive to complain that you can't force a broke pennyless country to indept itself. You can take all their lands, you can take all their money, you can take away their sovreignty, but you can't force them to give money they do not have. I could also question what clueless banker would lend money to a prince whose lands have been occupied by a foreign ruler.

Would warrant a pretty high interest rate, especially since you know the money isn't invested, but shipped abroad.