Final answer:
The Iranian borders were indirectly 'closed' during the 444-day Iranian Hostage Crisis following the 1979 Iranian Revolution, and previously, during the Allied occupation in World War II until 1946.
Step-by-step explanation:
The borders of Iran have been closed at different times due to various political and military conflicts. Most notably, during the Iranian Hostage Crisis, which occurred after the Iranian Revolution. On November 4, 1979, Iranian students, with the backing of Ayatollah Ruhollah Khomeini, seized the U.S. embassy in Tehran and held fifty-two American hostages for 444 days. These events were part of a larger geopolitical strife that included the Allies' occupation during World War II to safeguard against German access to oil, and the political turmoil surrounding the nationalization of oil during the 1950s under Prime Minister Mohammad Mossadegh.
The embassy seizure led to a rupture in U.S.-Iran relations, indirectly implying the 'closure' of Iran's de facto borders with the United States, as diplomatic ties were severed and tensions grew between the two countries. Furthermore, during the Allied occupation that lasted until 1946, Iran's borders were effectively under the control of foreign powers, creating another kind of 'closure.' The embassy staff was not released until the conclusion of the hostage crisis on January 20, 1981, the same day President Jimmy Carter left office.