Even though the US is dependent on oil, we do have a lot of alternate energy resources and a wealth of great minds (no, I’m not talking about Al Gore, quiet down). I believe the US could become free of our oil dependency if we really had to. Plus, if we get to keep all of the great minds from other countries that are currently over here studying and researching, well that’s a nice bonus too 
Following a horrible adjustment period, the Pacific islands would do okay – they would simply have to return to a subsistence lifestyle.
Likewise, following a period of possibly catastrophic social upheaval, I would think Indonesia and South Africa would both do fairly well as they have a wide variety of natural, human, and agricultural resources.
Oh man, Singapore would be SO screwed.
Does the OP’s scenario preclude the transmission of electricity and electronic transmissions across national borders as well? If so, that would play immediate havoc with multinational grid networks.
A few more points:
The U.S. would have to significantly convert to heating oil and [high-efficiency] wood-burning stoves, because we currently import much of our LPG [liquid propane gas].
All nations could shift much of their heating needs towards solar in various ways (such as passive heat-capture architecture) and wood/biomass, but not as easily towards solar cells for electricity. The manufacture of photovoltaic cells is such a high-tech and esoteric industry, and there would be a significant lag-time for many countries to implement it – and that’s only for those countries that have the necessary raw resources to build efficient cells. Silicon (sand) is ubiquitous, of course, but for really effective cells you need stuff like gallium arsenide, copper indium diselenide and cadmium telluride. Needless to say, simply manufacturing these compounds would be a significant industry in itself. (Solar water heaters, OTOH, are simple and effective energy savers.)
One big loser in the OP’s scenario: cosmopolitanism and heterogeneity in general, the unifying role played by the English language, and human rights. With no international travel, there’d be no wars, but also no humanitarian food drops, U.N. interventions, or “just” wars. No dictators would be toppled except by internal coups and revolutions; no [internal] genocides would be halted except by action of the same populations perpetrating them. No one would need study a foreign language in order to attend a foreign university or land a job overseas. English could continue to be a unifying thread in polyglot nations like India and Pakistan, certainly, but there would no longer be the particular inducement of living in London or New York for people there to learn it.
Questions for the OP:
How permeable are these barriers? Can animals migrate across them? Can poison gas be passed through them? Nuclear radiation/fallout? Oxygen? Will pollution from China’s coal plants still land on the US? Can we see through them? Hear sounds on the other side? (In which case, you will inevitably have information commerce/entertainment/etc.) What about the flow of rivers and underground aquifers/oil deposits? (I imagine you’d see upstream nations cutting off water to downstream nations, and countries pumping their aquifers dry so that their neighbors don’t get the water first.)
Would this tend to make now-unified countries fracture internally? Would the US fracture into the South and North and West? Would California secede?
On one hand, you would have no need for military expenditures if you had no external enemies; you would only need internal police. On the other hand, if larger states fracture, you might see terrible civil wars with military might remaining as important as ever.
Could the federal government in the USA hope to maintain the same kind of control and power without the threat of external enemies? I think you’d see states’ rights assert themselves very forcefully, perhaps to the point where the USA would become more akin to the EU.
A lot of how people would act under the no-trade rule would depend on their understanding of the new world order: would they “know” [the “perfect information” scenario] or guess that it was permanent, or would they be brewing cups of tea, sitting down on the couch with their friends, and waiting for it all to blow over? [the most imperfect info/wishful thinking/Shaun of the Dead strategy] 
Under perfect information, many people will be tempted to act in a manner less inhibited by custom, law, or the Geneva Convention.
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Would this tend to make now-unified countries fracture internally? Would the US fracture into the South and North and West? Would California secede?
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I strongly doubt it, provided that the Americans have perfect info (or guess as much) – if only for the reason that if an area managed to declare itself a sovereign state, its members would instantly lose much of their former freedom of movement! In which would you rather live, California or the other 49? And understanding that, the rest of the country would have every incentive to prevent seccession: the other 49 minus California means living with a lot fewer navel oranges, fewer porn flicks and video games, and a movie industry that largely consists of indie filmmakers based in NYC. And the seccessionist yahoos in the State of Disaster would have to realize that life without Tabasco sauce, Maine (or Florida) lobster, maple syrup or the latest-model Escalade would lose a bit of its appeal.
As that understanding sinks in, things would probably simmer down a bit.
Wow, you’re taking this seriously.
Ok. Animals can pass through them, but only undomesticated ones; no cattle, tame dogs, messenger pigeons, and so forth. The barriers are transluscent to visible light, but nuclear radiation, poison gas, and other forms of pollution are contained. If China (or the US) wants to screw up the environment, they’ll have to deal with the crap they create within their own borders. Natural things–rivers and so forth–flow as freely as before, but humans and their technology are utterly stopped. That’s ANY technology–you can’t send a care package on a raft down a river if the river crosses a natural border.
Ah, but you can divert rivers before they reach your neighbors, thus getting all the water for yourself?
So, with visible light, you’ll definitely have communication (and the possibility of at least trading entertainment … for more entertainment …). And it will be interesting to see the first Nuclear Winter contained to a single country.
Mongolia would do just fine. IIRC what resembles their economy imploded maybe 8 years ago, and much of the population went back to being herdsmen. The economy is doing a lot better now but not dependant on foreign trade to any major extent.
Would New Zealand even notice
It is already 1000km from its nearest neighbour. It has an agricultural base, and a small population for its landmass. It has a huge oceanic resource, and gas/oil reserves.
Sounds pretty survivable to me. But we would miss beating the Aussies and Poms at rugby 
Plus we are a nation of rugged individuals. Of course, I’d need some warning so I could get back before the borders closed.
Si
Duh. Porn. 
Doesn’t Israel produce olives? Can you use olive oil for a fuel source, and does Israel make nearly enough of the little things to have that be useful?
The fact that Alaska and Hawai’i are physicially divided from the Continental 48 could be problematic. Are there “lanes” that Americans could use to get from one to the other? Maybe a highway that Alaskans can drive up and down, but Canadians cross over via a translucent roof over the road? Would they effectively become seperate countries?
At least for the Alaska problem, the logical solution is for the US and Canada to join forces and become the Trans-American Consortium or the American Union or the United States of America, or some jingoistic-catch-phrase-y name like that. Canada gets a market for it’s exports, a source for high-quality beer (none of that crappy Canadian stuff, Shiners for everyone!) and of course, Knob Creek Bourbon. In the US, we get easy access to Alaska and it’s resources/peoples, comedians (Canada’s chief export to the US) and of course, all the beaver we could possibly want.
Addressed in the OP. Magical wormholes connecting Anchorage and Seattle, and, oh, let’s say Maui and LA.
I’d have to go with the U.S., with Canada a close second. Canada’s biggest problem is that, because we’re much smaller than the U.S., we depend much more on imports from the U.S. for staple goods. The U.S., being a global powerhouse economically, is less reliant on imports than a small country like Canada. The U.S. also has a much larger population, which is important if you want to build a really diverse internal economy.
On the other hand, Canada has more energy resources. We have all the Uranium we could need, and all the petroleum we could need. We have plenty of farmland for the population.
But the U.S. has it all already. It’s hard to think of a product you might need which you can’t find made in the USA.
The world economy as a whole would collapse to a tiny fraction of its current level, though.
Hmm. I wonder how greatly offshore activites would be impacted worldwide–isn’t a great deal of fishing/offshore oil drilling conducted more than 12 miles out? That would be outside the barriers. Japan and England (and the US in the Gulf of Mexico, or off the New England coast) might have some trouble there.
Food is the most important resource. Without food, everything else is worthless. If you’ve got too many people to support on the arable land you’ve got, you are going to have a lot of hungry people. That’s long-term. Short-term, you’d better hope like hell that you’ve got sufficient food on hand to last until you can switch over to an internal economy because hungry people will do anything, after a while, to eat. Famine and food riots are inevitable in all of the first-world nations; they all have populations above sustainable levels, with the possible exception of the US. That will cause massive disruptions, and if things get bad enough, it could possibly spell the end of any real government or even large-scale organization.
In all, I’d say that the US is probably going to be in the best shape. Low population density, has got a decent amount of all the necessary natural resources, but energy would obviously be the biggest bottleneck. In theory there are enough native resources to meet reasonable demands, but in reality using those resources would be difficult and would definitely take a while to implement. Making sure that there’s enough fuel for food distribution would be difficult. There would be civil unrest at best, and the government would probably have to impose martial law to quell widespread riots, even before the pinch was actually felt. I think that even though the US grows a significant portion of the world’s food there would still be famines and other problems related to distribution.
Brazil produces far more oil than it consumes and exports more food than it uses. They might actually be better off economically in some ways considering that they have a large amount of foreign debt that would never have to be repaid with the impermeable borders in place.
China will be in for some serious dark times again. They aren’t going to have the worst problem, but it would be no picnic, especially since the move to modernize has brought a lot more people into cities than was the case during the Great Leap Forward, when millions died due to more to reorganization and inept management than anything else. This would bring a similar crisis. Hopefully, having learned from experience, fewer people would die. At least, fewer would die right away. China does have way more people than it can feed by itself.
India, being less modern in some ways than many of the most populated countries, would probably do fairly well. Most of Africa is classed as “developing” which means that pretty much they don’t make anything anyone wants, and they’re too poor as a consequence to buy much of anything off the other nations. Like someone said earlier, they’d probably have the fewest problems.
Japan would be fucked. Seriously fucked. They would unquestionably be the worst-off of all the major industrial nations. Even with massive subsidies, protective tariffs, and other support in place Japan isn’t even self-sufficient in rice production. While you think of sushi and other seafood dishes as Japanese food, most of their fish come from halfway around the world, and they have exhausted many of the local sources. That’s a big one considering that seafood is the major source of protein in the Japanese diet, they import almost all of their meat, and most of their soybeans come from China. More than 90% of the population would simply starve, even if there were no other problems or violence. Given that, it’s hardly even worth considering that almost all of their energy is imported, the economy is almost entirely geared toward exports to survive, and almost all of their raw materials are imported also.
Most of the European nations would be pretty screwed too. The population densities in most of the countries are far higher than can be sustained without trade, and few of them have sufficient natural resources to live. I’d give Germany and France among the western countries the best chance. I don’t know enough about eastern European countries to give good guesses about them, but they might be better off than some of the more modern western countries simply because the scale of their economies is lower and so they’re used to doing more with less.
While countries like Australia and New Zealand could survive due to their natural resources, they would have to reorient their economies considerably to maintain anything like their current standards, because so many of their manufactured goods come from overseas. They might be able to do it, but it would take some time, and the small populations would mean relatively poor economies of scale for a diverse manufacturing sector.
I’m with Sam Stone. I think the US has the combination of natural resources, developed industry, and population to make the best of autarky.
I think Australia would be pretty right. We don’t have vast oil reserves but do have lots of coal and a lot of uranium for power stations. No worries with food. Maybe the technology to build nuclear power stations would be the problem.
The key to having enough food is not how much arable land you have, but whether you can maintain a high technology mechanized farm industry. To do that, you need to be able to build your own tractors, tractor engines, ball bearings in tractor engines, metal to make the ball bearings, factories to make the metals, mines to dig up the ore required…
Maintaining a high-technology society requires tremendous resources. And not in the sense of cash, but in the sense of having enough educated, competent people to be able to make all the things required. Given the diversity of materials and products you need, that’s a LOT of people. I don’t think a 20 million person country could do it.
That’s why the U.S. would be best off. It not only has the natural resources, but it has a large diversified industrial base and a huge population to draw from.
The countries that would be best off would be the ones with the biggest populations. India, China, the U.S, etc.
If the industrial economy crashes and a country can’t maintain its high-tech infrastructure. There will be widespread starvation and the economy will plummet to 3rd world status as 90% of the people head back into the fields to help grow enough food to survive, further abandoning the high-tech jobs.
There’s no country on Earth that could a escape a massive economic depression - even the U.S.
Don’t India and China already have problems with feeding the population? Australia does have a vehicle manufacturing industry including cane harvesters etc. Although high tech makes things easier, it is not necessarily essential. Better strains of plants means far more return per acre in any case.