The doctrine enunciated by President Jimmy Carter in 1980, stating that "An attempt by any outside forces to gain control of the Persian Gulf region will be regarded as an assault on the vital interests of the United States of America, and such an assault will be repelled by any means necessary, including military force." The Carter Doctrine, although it was not formally invoked, was put to the test after Iraq invaded Kuwait in 1990. The resulting Persian Gulf war in 1991 showed that the U.S. did indeed regard the attempt by a belligerent country to gain control of more than its allocated share of the region to be an assault on the vital interests of the U.S.