The Persian Gulf region continued to be regarded as an area of vital importance to the United States during the Cold War. Three Cold War United States Presidential doctrines—the Truman Doctrine, the Eisenhower Doctrine, and the Nixon Doctrine—played roles in the formulation of the Carter Doctrine, which stated that the United States would use military force if necessary to defend its "national interests" in the Persian Gulf region. Carter's successor, President Ronald Reagan, extended the policy in October 1981 with what is sometimes called the "Reagan Corollary to the Carter Doctrine", which proclaimed that the United States would intervene to protect Saudi Arabia, whose security was threatened after the outbreak of the Iran–Iraq War. Some analysts have argued that the implementation of the Carter Doctrine and the Reagan Corollary also played a role in the outbreak of the 2003 Iraq War.