Suppose that I lend money to a business or individual associated with the government in Russia, Venezuela, or some other country. Suppose that by the time the debt is due, my country of citizenship or residence business or individual has declared sanctions on my debtors and prohibit me from doing business with them. Would the sanctions prevent me from legally getting my money back?
If it is illegal to transfer money between the jurisdictions then any contract that requires that to happen is unenforceable.
This is a subset of "sovereign risk" in a trans-national deal.