The Carter Doctrine was a 1980 assertion by US president Jimmy Carter of a vital American interest in the Persian Gulf region.
It was prompted by the Soviet invasion of Afghanistan and the instability in the Shah's and subsequently Ayatollah Khomeini's Iran. The USSR came with the so-called Brezhnev Doctrine in August 1968, trying to justify Soviet domination over its neighbours (not only those in Eastern Europe as many of my fellow Europeans seem to think). The Soviets stated:
"When forces that are hostile to socialism, seek to reverse the development of any socialist country in the direction of restoring the capitalist system, when a threat to the cause of socialism in that country appears, and a threat to the security of the socialist community as a whole, that is no longer only a problem for the people of that country, but also a common problem, a matter of concern for all socialist countries."
This text was used to explain the Soviet invasion of Afghanistan in 1979 in an effort to keep in power Communist forces beset by growing civil war there. In January 1980, the United States of America formally announced its response with the Carter Doctrine, which stated that:
"An attempt by any outside force 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."
Clearly the immediate event which precipitated Carter's new policy, and motivated him to develop a containment strategy for the Persian Gulf area, was the Soviet invasion of Afghanistan. However, Carter had been growing restless for months because of the mounting Soviet and Soviet client pressure in the Third World and the relentless Soviet arms buildup in Europe.
The consequences of the Carter Doctrine towards the situation in the Gulf area are not very clear. Among historians the doctrine is rather used as an example to Carter's flaw in clear foreign policy, unlike the White House law, "first and foremost, every administration must have a clear, consistent policy toward the Soviet Union". The Carter Doctrine showed the United States a president, who, pushed relentlessly by external events, had to abandon the basis of his initial non-confronting policies. Ten months later he was soundly defeated for reelection.