On 27 December 1979, two Russian doctors working at the Soviet embassy in Kabul received an urgent call to help Hafizullah Amin, the President of Afghanistan. Together with his children and several members of the Afghan Politburo, Amin had fallen unconscious after a lunch of vegetable soup, prepared by Soviet cooks. Unbeknownst to Amin, he should have been dead two weeks earlier, save for the fact that the effervescence of his Coca-Cola had neutralised the poison it contained.
Grasping that Amin had been poisoned, the doctors managed to resuscitate him from a coma. By the evening, Amin was well enough to inch around his palace, although he soon found that the phones were dead. After gunfire erupted inside the palace, heavily-armed Soviet commandos burst in, shooting the President and killing him (and his son) with a grenade. One of the doctors was killed by what he assumed were Russians coming to help prevent a coup. In reality, 80,000 Soviet troops were spreading out of Bagram air base and pouring over the Afghan northern border. Many of them were Central Asian Muslims, a placatory gesture that underestimated the hostility between Pashtuns, Tajiks and Uzbeks.
The invasion decision had been taken by the Soviet Politburo on 12 December. Leonid Brezhnev had been outraged when in September Amin not only ousted President Nur Mohammed Taraki, but reneged on promises to send him into exile. Taraki, whom Brezhnev had recently welcomed to Moscow, was killed in a Kabul jail, allegedly because he had tried to assassinate Amin.
The Soviets were more concerned with the wider repercussions of this internecine feuding within the Afghan Communist Party. Moscow thought that the party should broaden its support before embarking on social change. Instead, Taraki and Amin had pressed ahead with reforms, including expropriating the farms of feudal landowners, closing mosques and educating girls. This triggered a fundamentalist backlash, to which Amin had responded with abductions, torture and murder. Worse, the KGB residency reported that Amin was engaged in shadowy dealings with the US. Moscow feared that having lost the Shah of Iran, the US might be seeking compensatory influence in Afghanistan, with rippling effects in Soviet Central Asia.