In SF, we tend to look a few hundred years into the future, and deal in starships and extrasolar worlds. I've always wanted to look out into the Solar System, the real estate of the Real Future, and I've been looking over George Friedman's shoulder, into his crystal ball, particularly his last two books, 'The Next Decade' and rereading 'The Next 100 Years' (they sound like the same book, but the difference of focus is key, and he looks more closely at Brazil in 'TND', a country I expect to see as a major space power), trying to come up with a new near future setting, one that doesn't involve hand-wavium and near-magic, but does involve the development of the Moon and the NEAs...
He thinks we will have to re-fight the cold war with Russia, in miniature, on more time... supporting Poland and Eastern Europe against a resurgent Russia, while Germany and Western Europe stays out of it. Later, Eastern Europe and Turkey would expand into the region, physically or at least economically dominating things, especially Turkey, whose time has come round again, thanks in part to the mess we have left in Iraq and the Arab Spring (too soon for GF to have added that to his speculations in 'The Next Decade', but I can read the tea leaves a little bit, too 8-).
Brazil, in South America, and Angola, in Africa, both have a special relationship (BrazAnga!). They are Portuguese-speaking countries, and Angola has cheap labor and resources Brazil needs as it reaches its internal limits and looks around to outsource some of its economy, like we did, to China and elsewhere, and which China in turn did to SE Asia. I think that maybe in the late 21st C, the US, which considers the Pacific to be its personal lake, at least from Hawaii back to the mainland, and the North Atlantic to be a 'pond', will acquiesce to Brazilian South Atlantic power. Turkey will be a regional naval power, from the Black Sea to the Persian Gulf, all places that the US is less and less interested in any more. India will probably be our proxy in the IO by the late 21st Century.
Coastal and South China will call the shots in the future, not Beijing. It is cruising for a bruising right now, crony capitalism on steroids, with bad debts at 25% to 40%, twice what Japan experienced in the 90's. The only question is how far it will fall apart, and how far the central government will go to crush dissent a generation after Tienamen Square.
By my musings, the US is still the big guy at the end of the 21st C, with a 1/4 Quadrillon dollars GNP, but the Gross World Product may be $1.5 to $2 Q at this point, because I'm sure everybody who can is growing just a little bit faster than the Big Dog, over a long time. Even if the GWP is $1 Quadrillion, no worries; that's still ~20 times what it is today, and it implies a new source of energy, probably offworld solar or He3, or both. For the US, we'll be fracking for natural gas and using more coal in the near future, and dealing with the environmental damage, as and when. Per-maybe-haps we'll come around to nukes in a can, and 'burn' up some of our nuclear waste before that ticking time bomb goes off; maybe. But at some point we will need to look up, and go up and out, to secure the new source of power we'll need in the next hundred years.
The numbers are pure fantasy, grounded in my imperfect understanding of what I've read and my prejudices, but they imply that all but one of the 'Next Five' will be in Eurasia- Turkey, India, (South) China, and Japan, all nicely balancing each other so that there is no dominant Eurasian power. Brazil is probably more troublesome, a South Atlantic power with a foothold in Africa, but Nigeria, South Africa and Argentina are available to oppose it, and Poland (which will lead Eastern Europe against Russia, get lots of goodies, but not all, after it falls apart, and protect a declining Western Europe by default), Iran, Indonesia, Vietnam, and the Philippines will serve as buffer states elsewhere. Australia will probably be looking for a friend, now and always, and we can keep her, if we play nice. Turkey controls much of the Middle East and as much of North Africa as it can, hemmed in by Poland, Nigeria and Iran, and rattling sabers with India.
What I've taken away from the two books looks like this- China and Russia crumble due to wars and internal troubles. Russia is dismembered and marginalized by Turkey and Eastern Europe; Japan gets Maritime Russia in the West as a protectorate. It also develops interests in coastal China, as does everybody else. As time goes on, Turkey and Japan become regional powers, offset by Poland, Eastern Europe, and Iran in the West and by India, China and United Korea in the East. Turkey probably guarantees Japan's access to Saudi oil for a little while longer, but everybody will be kicking the hydrocarbon habit eventually.
In the thirties Brazil is growing as a power across the South Atlantic in Angola and southern Africa. The US moves to oppose this through Argentina, South Africa and Nigeria, already a regional power and now beginning to really grow, industrially, the fruits of stability and investment in education and infrastructure is paying off in a take-off like Brazil now. It has a similar size population, but a long way to grow to catch up.
I have Brazil growing explosively in my spreadsheet, so it will look like a threat on our front door step, too close to ignore. The US will over-react, leading to a nazi-fication of Brazil in the media, and we will probably be preoccupied with the South Atlantic while Turkey is growing into a potential problem. GF has Turkey and Japan trying to develop spheres of interest in Eurasia, which the US will oppose, having seen off Russia and China as threats and we never want to see any one country dominating the 'world island', and becoming a threat to American power. If they ally and act together, as GF have them doing in 2050, they could achieve their goals, or just a likely get smacked down. The US would go to India, a resurgent and re-aligned China, and smaller regional powers like Poland, as counterweights, allies and proxies.
In the long run, just a gut feeling, but I think that Brazil and Japan will be space powers. I don't see Japan going away, but I do see it having another 'lost decade' if it does go down to defeat, as GF has them doing in the 2050 War. China, India, and Turkey, too, for I don't think you can grow in the last half of 21st Century without space power, either force or energy. Countries that don't go into space will eventually be marginalized, like Russia, and become either victims or quaint backwaters.
In 2050 the 'Big 4' are the USA, Japan and China, who have swapped places again, followed closely by Brazil. Again, these numbers are pure fabrication, but I can work with this. The US economy is three times as big as it is today, and the population is a third larger (there are about half a billion people in North America, just as the population of Europe has fallen towards half a billion). All three are about half as big as the US, and bigger, economically, than the USA is today, great powers with suborbital space planes, oh my. Turkey and India are not far behind; watching each other uneasily in Central Asia and the Indian Ocean, plus their combined weight is about equal to any of the preceding three. The next five economies after the US add up to nearly twice its economic power.
George Friedman doesn't address this, but I will. From this point on, space power and dominance becomes imperative. The US will still try to control the seas, as a great trading power, but in the last half of the 21st Century we might see the US making territorial claims on the Moon because it is the new high ground. As an American, I say- 'Sweet!' But as a human being, I say- 'Oh shit.'
My model has the US growing quickly in the 50s and 60s, fueled by cheap energy and lots of it, plus developing heavy orbital industry. China rides along, Japan turns aside for a little bit, and Brazil also loses its way for a while. Turkey and India both grow quickly, with Turkey growing into its empire and realizing untapped potential in a stabilized Middle East. India is still industrializing on the ground, but growing into space as well.
China pulls ahead of Japan again, Brazil powers up and gains on China, a long stern chase through the seventies and eighties. During this time, GF sees a crisis unfolding with Mexico and the borderland in the Southwest, so I throttle the American economy back a little. Seven decades from now it's ten times as big. As it is now, China's is nearly half as big, as is Brazil's. These two are no threat to each other and share enemies, plus a resentment of nearly a century of American power; its hubris and carelessness. They are both interested in space power, and may force some sort of concession. It's hard to imagine the balance of power system falling apart, but they might back each other against the USA, leading to a world of squabbling great powers that can make the former superpower back off.
Oh shit, squared.