In 1979 the Soviet Union invaded Afghanistan to stop it falling into the US sphere of influence. The war would prove expensive, damaging to morale and damaging to Soviet relations with the Muslim world, the US, Europe and China.
The Soviets knew invading would be a mess, though they underestimated just how unhappy it would make the rest of the world - they'd been putting off military intervention all through the 70s and only went in when they'd reached a state of panic about the situation in the country (panic fuelled by KGB "dodgy dossiers").
So what if they put off intervening for a bit longer, maybe because their relationship with Hafizullah Amin worsens faster or maybe because Brezhnev keeps a few of his marbles and keeps saying "no" to the plan to invade Afghanistan until it is too late for even Andropov to think an invasion is worthwhile.
So what happens next?
For a start, there are no Carter sanctions on the Soviet Union. This means trade continues unimpeded and the USSR continues importing high-tech western goods (like large diameter oil pipes) and licensing western technology at the same rate it was over the 70s. Overall, this is probably good for the Soviet Union, and the economic crunch of the early 80s will be a little less severe.
That, together with avoiding the material and human cost of the Afghan war may mean the Soviet Union can survive into the 90s.
There will be no Olympic boycotts (does this have much of an effect long term?)
Relations with China steadily improve over the 70s and 80s, instead of going through a temporary freeze from 1979 to when Gorbachev arrived, I'm not sure what effect this would have though. Thoughts?
The Amin regime in Afghanistan may well switch sides to align with the US (there were moves to indicate this was about to happen when the Soviets intervened in OTL) - which would mean the USSR borders yet another US ally, but it also means that the Islamic militants that the Pakistani ISI has been supporting are now the enemies of the American-aligned regime and the enemy of the enemy of the Soviets. Might some Taliban re-brand themselves as "Islamic Socialists" to try and gain Soviet patronage? (My bet is yes, at least for some, the Taliban groups have always been more concerned with their own fractious tribal politics than external ideologies.)
What effect does no Soviet invasion and an American-aligned Amin regime have on the Iranian Revolution? The Soviet invasion was a big deal for Iran and was a major reason for the early hostility of the new revolutionary Iran towards the Soviet Union. No invasion wouldn't make Iran a friend (too much bad blood for that) but it may mean Iran is more receptive to Soviet overtures earlier (say, in the early to mid stages of the Iran-Iraq war, as opposed to OTL's warming of relations which came only at the very end of the Iran-Iraq war). Iran and the Soviets may also find common cause against what is likely to be an increasingly nationalist and Sunni-centric regime in Afghanistan.
Might all this also lead to a warming of Pakistani-Soviet relations? Afghan nationalism was rather preoccupied with annexing the Pashto speaking borderlands of Pakistan (this was also a big source of friction between the Soviets and several Afghan leaders, since the Soviets had no interest in being associated with an invasion of Pakistan). If the US ends up backing Afghanistan, Amin's regime is likely to become increasingly nationalist, intensifying friction with Pakistan.
And what role might India and China play? I would have thought they would be friendly to the Amin regime and eager to ensure Afghanistan doesn't fall to the Taliban. I'm not sure how able they'd be to intervene however.
Finally, whither Afghanistan? My gut feeling is there's no happy ending here. Though perhaps, things might be slightly less bad than OTL. Once Iran falls, the US is not going to be able to help Afghanistan against Pakistan and they'd never be interested in doing so. My bet is that the US would be out within a year or two, likely Amin loses power at the same time. The replacement would either be a Taliban regime (would they be as extreme if they won power earlier?) or a military dictatorship. Things could get more interesting if India and/or China are able and willing to intervene.
Anyone have any thoughts on this one?
fasquardon