Could the Soviets encourage mass immigration anytime post 1945 as a way of gaining both high and low skilled labor
how many immigrates could they gain over the cold war, especially if the Soviets allowed easy immigration from their third world allies.
What would be the social,economic, and political impact on the Soviet Union
What happens after the soviet union collapses
The Soviets did encourage immigration after WW2, at least for Armenians. It was a sordid con.
People would come into the Soviet Union, find conditions far worse than advertised (worse even than their former homes and given that most were coming from Turkey, they weren't exactly coming from a great situation), but unlike a normal country, immigrants weren't free to leave and the KGB would fake letters to the families of immigrants to paint a rosy picture of their new lives and encourage the families to immigrate too.
Not with Stalin in power no one sane would voluntarily move to live under that monster.
Funny thing is, sane people really did emigrate to the Soviet Union. And not just the Armenians mentioned above. Before WW2 people from the US and Western Europe emigrated for a better life during the great depression (as well as some degree of ideological fervour, to help build the new worker's paradise), 3rd World nationalists and socialists emigrated there for safety and to get educations. Needless to say, both groups were heavily targeted during the purges. And since the Soviets weren't exactly advertising their crimes, people still came. This wave of migration mostly petered out simply because the Soviets couldn't build houses fast enough, so the bureaucracy scaled back their hiring and encouraged immigrants already in the country to leave, there seems to have no shortage of ignorant optimists or wilfully blind fools who'd have been willing to migrate had the Soviets been open to more migrants (though of course, once the Great Depression had ended, I suspect this would have been different).
The Soviets also have more than enough unskilled labor. No incentive there.
Not after WW2 they didn't. The Soviets were short of all kinds of manpower after the war. Which is exactly why they were in OTL encouraging immigration (under awful conditions due to shortages of shelter).
They also retained WW2 PoWs too long and extracted coerced labour from their part of occupied Europe. Really it was slavery, and not what I'd class as immigration but the demand for such slavery does rather indicate that the Soviets really were in need of manpower (though some of these forced labourers - a very few who wanted to stay and were allowed to stay - would stay in the Soviet Union and build lives and families, so adding themselves to the Soviet population proper).
I think the real problem for Soviet immigration is that the regime wanted to be in control. Even as a Soviet citizen you needed official permission to move to a different region of the Soviet Union. Foreign nationals moving into the Soviet Union faced a wall of paper. Also, for the most part the Soviets didn't seek permanent immigrants. The Communist countries traded manpower, with bureaucrats negotiating with each other about how many thousand men to trade with their opposite numbers for how many years in return for however many shoes or whatever (I've said it before, but the Soviets and their daughter regimes had the most awkward way of trading you could imagine), so Vietnam, for example, became an important source of immigrants for the USSR and for Poland after the 60s, Mongolia imported Chinese labour (paid for by the Soviets) but this wasn't supposed to be permanent. Permanent Vietnamese communities did form, but they were made up of supposedly temporary workers. Earlier waves of "traded" labour (which as mentioned above was more slavery than economic migration) from Eastern Europe to the Soviet Union after WW2 had mostly been returned to their native countries (sometimes unwillingly as some of these men had lived most of their adult lives in the Soviet Union, had friends, homes, decent jobs and sweethearts or even wives only to be forced out of the Soviet Union when they were no longer wanted). Even so, immigration flows into the Soviet Union were growing quickly and as the Soviet Union aged, it became more relaxed about ignoring people who overstayed. It's quite possible that had the Soviet Union survived to the present it would have experienced a surge in migration like the capitalist world has over the last 30 years, with similar anxieties about cultural displacement burgeoning.
And entwined with bureaucratic control, there's the constant shortage of housing in the Soviet Union. As mentioned above, this seems to be the main reason why the Soviets stopped trying to recruit immigrants during the Great Depression (and they even encouraged many immigrants to return home). After the housing stock was worse than decimated by WW2 (something like 1/3rd of the total housing stock had been reduced to rubble), the situation was even worse. And since the regime had relatively strong control on labour inflows and outflows from the Soviet Union, it was relatively easy for the regime to expel guest workers or deny immigrants entry as a means of reducing the scale of the housing crisis. The sheer scale of the problem makes it hard to imagine solutions that would create enough slack to allow mass immigration.
Perhaps in a TL where collectivization were avoided, meaning Soviet citizens are slower to move from the farms to the cities there's both the demand for labour and maybe house-building can proceed fast enough to allow a major influx of immigrants during the Great Depression (and while no collectivization slows the early stages of industrialization under Stalin, the regime doesn't destroy its credibility as fast, the Purges are probably delayed and there's a good chance that the later stages of Stalin's industrialization before WW2 go much faster than OTL, oh, and millions of Ukrainians, Russians and Kazakhs avoid the awful deaths they suffered in OTL).
Another pre-war PoD could be that Stalin simply decides that the need for Communist true believers is such that foreign Communists should be encouraged to migrate to the worker's paradise, rather than remain in their home countries to act as 5th Columns. A similar PoD, but post WW2, could be Stalin or one of his successors deciding to encourage Communists to migrate to the Soviet Union from the West as a way to reduce tensions/get good Communists into a place that they'll do more good. I have a hard time seeing either of these being sufficient on their own to drive mass migration, but perhaps they could contribute (of course, I suspect most foreign Communists would rather stay where they are when they have friends, jobs, families and of course, revolutions to spark at home).
A 1940s PoD could be that WW2 is simply less destructive than in OTL, meaning the Soviets recover from the home-deficit caused by the war sooner, meaning that there is more space to allow guest workers to remain in the country and to accept new immigrants meaning the growth of immigration to the Soviet Union is accelerated by about 20 years and the Soviets have significant populations of settled former guest workers from Eastern Europe and China forming from the late 50s onwards.
It's more difficult to get the Soviets to accept mass migration with a PoD between 1945 and 1989. Especially because I think the only way it'll happen is for the Soviets to pursue it as a policy goal. While there are poor countries where life is even worse than what the post-war Soviet Union can offer, most of those countries are so poor that people can't afford a ticket to the Soviet Union out of their own resources until 1970s, and even then, the list of countries with people who can afford tickets to the USSR but also have lower quality of life than the average Soviet citizen is a fairly short list. And for most of those countries, it's just more convenient to emigrate to the West.
China may be willing to send many more guest-workers to the Soviet Union before the Sino-Soviet split (I'd like to emphsize though, there's little reason Chinese guest workers would form much of the labour force in Siberia - most of the work that is to be had is in the western USSR so we're talking about big Chinese minorities in Moscow, Kiev and the Donbas, not Irkutsk and Vladivostok). A TL where there's no Sino-Soviet split (say, because there's no Khrushchev gaining power, or Khrushchev is deposed much earlier) could also see Chinese guest worker flows growing over the 60s and 70s.
The Soviets might also be motivated to seek more immigration from Africa and the Middle East. Especially, in the 70s and 80s, of various stripes of Oriental Christian in an effort to balance out the growth of Muslim populations in the USSR. Also, the USSR might be motivated to encourage African migration in order to build up a prominent black Soviet community to better boast about in propaganda (of course, the Soviets could and did boast about OTL's black Soviet community, so this isn't a sufficient reason in and of itself).
Another idea is that the Soviets force much deeper economic integration on their Satellites and also favour a policy of concentrating population in Soviet industrial centres, meaning much more ComEcon guest labour in the Soviet Union. A further development of this could be the Soviets getting their 3rd World clients to pay for the weapons and development aid they were buying with guest workers. (Again, all of these people need houses somewhere though.)
Speaking of which, the Soviets nationalizing house building might help alleviate their shortage - when the USSR fell, houses were built by enterprises for their workforce. This, as you may expect, was inefficient and fostered corruption. So perhaps house building being done by specialized enterprises with their own workforces would be a better way of doing things? I'm not sure. Enterprises not building the houses does greatly reduce the ability of enterprise managers to blackmail the central government, but that doesn't necessarily mean that much more houses could be built than OTL.
And of course, if the Soviets are successful and get mass immigration going, they are going to end up with an embarrassing dependence on Western food more quickly.
What would be the social,economic, and political impact on the Soviet Union
This really depends on how the Soviets have done things.
IMO the easiest solutions to the Soviets economic problems involve mass immigration, so one possibility is that the Soviets survive and thrive due to lucky policy choices. However, I can also imagine situations where there is mass immigration but the impacts on the Soviet Union are neutral or negative (though they may bear fruit for the post-Soviet successor states).
Culturally, mass immigration of Orthodox Ethiopians will be very different from the mass immigration of Afghan Muslim refugees or Chinese guestworkers.
For example, the Soviets built cultural centres for Vietnamese immigrants that provided a wide array of services to that immigrant community, including holding bazaars every week where anyone could set up a stall and buy and sell goods. That's the sort of thing that had been beaten out of the general Soviet population under Stalin, so one impact of serious Vietnamese mass immigration could be the re-emergence of self-employed business as the Soviet Union liberalized and a large Vietnamese population started to interact more with the general population. By comparison, Eastern European immigrants (judging from the stories of the children of Soviet-era migrants I've been told) lived much like their Soviet peers, so even more Eastern European immigrants don't reintroduce small business into the Soviet economy.
So it's hard to generalize, immigration will have different effects based on what the communities of immigrants are and what the Soviet policies towards those communities are.
fasquardon
