The OP’s scenario implies that with no travel between countries, no one could return to their country of origin, either. That would not only settle the immigration issue for the U.S. (presumably, all Mexicans will become naturalized citizens and pay taxes, and a wall would no longer make any difference), but strand millions of tourists and students where they are now, and millions of guest workers would be stuck in the Persian Gulf states and elsewhere.
Dubai would transform overnight from a jet-setter’s and venture capitalists’ paradise to a soon-to-be-starving ghetto in which the disenfranchised guest workers (from Pakistan, India, Bangladesh, Egypt, etc.) would considerably outnumber the native, wealthy Gulf Arabs. That could make for some interesting turmoil and draconian violence, to say the least. At least Saudi Arabia has invested in some very costly agricultural projects, reliant upon water produced by desalinization. I dunno if they produce anywhere near enough to feed their own population, let alone the guest workers, but it’s a start. OTOH, I doubt if a civilized veneer in Dubai could hold out for as long as it would take for the imported liquor to run out.
Some of these countries might be able to sustain their populaces in terms of minimum caloric consumption, but not without suffering cataclysmic socio-political disruption, even revolution. China’s underprivileged peasantry of old has been migrating to the cities, for manufacturing jobs, by the hundreds of millions. Take away global trade and those jobs disappear (as well as the food imports) – and the Chinese CP won’t have to order those peasants back to the countryside at gunpoint, but use those guns to retain a threshold of urbanites in the cities.
[And that stat of China’s grain imports from Australia only adds up to about 3 lbs. per person per year – an insignificant amount by itself. Of course, that’s not all they’re buying, so they would admittedly be more affected than that.]
One country that should fare pretty well, provided it can elect a competent government, is Venezuela. They’ve got the oil, the tropical climate, are probably not overpopulated relative to their agricultural capacity and other resources (such as fresh water and marine fisheries). They’ve also got a horse’s ass for a president… thanks to Hugo Chavez’ insistence on price controls, food shortages are increasing in stores. Not because of famine, but because farmers and grocers are reluctant to part with the goods when doing so will cost them money.
I’d be skeptical about the long-term ability of France, Britain, and Japan to maintain their electricity generation without imported uranium, as they’re all very dependent upon their nuclear power plants. They might be able to finesse a smooth transition to wind, hydroelectric, solar, biomass, and tidal power as their fuel rods wind down, but eventually their nuke plants would become worthless.
Sub-Saharan African nations currently beset with high rates of HIV, malaria, etc. would have to ramp up domestic production of lifesaving pharmaceuticals or suffer accordingly. But some of these countries, despite their relative poverty and frequent political instability, are surprisingly well-situated for certain high-tech industries, because of their wealth of precious metals like titanium, platinum, gold, etc. (Not that there’d be a high demand for jet aircraft in a zero-international-trade world, but still. In the very long run, after they’d gotten over the humps posed by the no-trade thing and HIV, they could exploit that capacity.)
And any country with a tenuous grip on caloric self-sufficiency and which also exists in a monoclimate or has a monocrop agriculture would be critically vulnerable to famine. North Korea (droughts), Bangladesh (floods), the Horn of Africa states (drought, locusts)… most of these people would be doomed at the first catastrophe. By contrast, it’d be a very unlucky year that would see persistent crop failure in the USA, from the East coast to the West and all points in between, of our grains, fruits, and vegetables.