The 1970s and early 1980s saw the onset of stagflation. The United States supported Israel during the Yom Kippur War; in response, the country faced an oil embargo from OPEC nations, sparking the 1973 oil crisis. In 1979, President Jimmy Carter brokered a peace treaty between Egypt and Israel, marking the first time an Arab nation recognized Israeli existence. After his election, President Ronald Reagan responded to economic stagnation with free-market oriented reforms. Following the collapse of détente, he abandoned "containment" and initiated the more aggressive "rollback" strategy towards the Soviet Union. The late 1980s brought a "thaw" in relations with the Soviet Union, and its collapse in 1991 finally ended the Cold War. This brought about unipolarity with the U.S. unchallenged as the world's dominant superpower.