When it comes to resolving debts, it's always the same anywhere. Debt after all, is just a measure of how much someone owes a favor, and money the opposite; a measure how much someone is owed a favor. In other words, debt/money is nothing but a measure of exchanging favors (ie trade).
So when it comes to resolving debts between nations, it is resolved in the very same manner: via trade.
However, forcing a foreign nation to uphold their trade agreements (debt obligations), or even domestically speaking, is a separate matter entirely (ie the matter of taxing). As far as foreign nations go when they don't uphold theirs, you can engage in war and confiscate things, and/or you can change trade agreements. These are actually the very same options you have domestically speaking (repos / taxes).
