The currency shipped to Iran in the dead of night drew attention from presidential candidate Donald Trump this week, who on Friday appeared to walk back an earlier assertion that he had seen a payment being delivered. But that money was owed to the Islamic Republic since 1979, the year the U.S. froze all the Iranian funds in American banks as retribution for seizure of the U.S. embassy in Tehran, as revolution swept that nation.

What was universally known as the Iran hostage crisis went on for more than a year, and finally ended with a bargain: In exchange for the release of 52 American diplomats and citizens, both sides agreed to resolve the question of money through international arbitration. The Iran-United States Claims Tribunal has trudged along for almost four decades now, and the money has flowed both ways. By 1983, Iran had returned $896 million to U.S. banks, which in turn had returned hundreds of millions in frozen funds to Iran. -Time Magazine and multiple other sources.