On November 12, 1979, President Jimmy Carter responds to a potential threat to national security by stopping the importation of petroleum from Iran.

Earlier that month, on November 4, 66 Americans at the U.S. Embassy in Tehran had been taken hostage by a radical Islamic group. The alarming event led Carter and his advisors to wonder if the same or other terrorist groups would try to strike at American oil resources in the region. At the time, the U.S. depended heavily on Iran for crude oil and Carter’s cultivation of a relationship with Iran’s recently deposed shah gave the radicals cause, in their view, to take the Americans hostage. Not knowing if future attacks were planned involving American oil tankers or refineries, Carter agreed with the Treasury and Energy Departments that oil imports from Iran should be discontinued immediately. This ended America’s formerly friendly association with the oil-rich nation.

The U.S. and Iran had previously enjoyed a healthy diplomatic relationship; Carter had even enlisted the Iranian Shah Mohammad Reza Pahlavi’s help in reconvening peace talks between Israel and Egypt. Carter also sought Iran’s help in supporting nuclear non-proliferation talks with the Soviet Union. Carter and the shah affirmed their desire to collaborate on alternative energy and oil conservation. He even once toasted Iran under the shah as “an island of stability” in the Middle East.

While Carter and the shah planned closer collaboration on energy issues and the Middle East peace process, an Islamic revolution was brewing in Iran. The shah, who was reviled by the revolutionaries as catering to evil Western influences, was deposed in January 1979 and replaced by a clerical regime led by the Ayatollah Khomeini. In October 1979, the exiled shah came to the United States for cancer treatment. Carter’s hospitality toward the shah enraged the group of radical Iranian students who, on November 4, stormed the U.S. Embassy in Tehran and took 66 Americans hostage.

The ensuing hostage crisis, which lasted 444 days, eroded Carter’s popularity and he lost his bid for re-election to Republican Ronald Reagan. Reagan went on to serve as president from 1981 to 1989.