in December confronted with an increasingly chaotic situation and the pending triumph of Islamic rebel forces ,Russia sent an invasion force of more than 50,000 soldiers into Afghanistan and brought babrak karmal, head of the pro-soviet parcham faction, back from exile to serve as the new president.
carter denounced the soviet invasion. he halted the SALT II ratification process, suspended the sale of high technology to the soviet union , imposed a grain embargo , and called for the establishment of a rapid deployment force. carter also issued a warning, which came to be referred to as the carter doctrine, in his 1980 state of the union address. he stated that any "attempt by outside force to gain control of the Persian gulf region will be quickly repelled by any means necessary including military force"
the harsh tone of carter's response reflected more than just his disillusionment with the soviet union . it also reflected his administration's frustrations in dealing with the new rulers of Iran , who one month before the soviet invasion of Afghanistan had seized the American embassy and taken American hostages. with only a slight period of interruption, Iran had been ruled from 1941 until 1979 by one of America's most loyal third world allies, mohammed reza shah phahlavi. that interruption came in 1953 when the shah was forced into exile as Iranian nationalists seized power. he was restored to the throne largely through the efforts of a CIA-inspired coup. over time the corruption and repression of the shah's rule reached the point where he became dependent upon the military and his ruthless secret police. the SAVAK ,to say in power. even this proved to be insufficient as the 1970s drew to a close and Iranians took to the streets demanding reform.
the carter administration was caught off guard by the shahls rapidly mounting political troubles. it had become an article of faith that the shah would remain in power and that Iran would be pro-west. after first backing the shah, the carter administration unsuccessfully urged him to negotiate with his opponents. the most important opposition leader was the ayatollah Khomeini, who was in exile in france and returned to Iran on January 31,1980 to take over the reins of government. the shah had left Iran in the middle of the month. the carter administration first weighed letting him come to the united states but reconsidered due to fear of the reaction it might pro-voke in Iran . in October, at the urging of Kissinger, Brzezinski, and david Rockefeller,who headed chase manhattan bank, and over the object of the U.s. embassy in Iran, carter agreed to let the shah come to the united states in order to receive potentially life-saving medical care. two weeks later the embassy was Iran to stand trial