In budgets, any estimates more than 3-5 years out is simply 8-Ball conjecture. Elections and economies are fickle things.
For strategy and Fleet planning, you need to think at least 10-years with a stretch to 20 off in the mist.
Demographics? Well .... that has about the same timeline. No one 20-30 years ago would have had a clear picture of the falling birth rates overall - Malthusians were still the rage - but people were close. Though the exact numbers have a very wide standard deviation - I think the macro ranks and positions are probably a lot closer. That is where you need to ponder.
So much of our thought about the global system remains in the mechanism of the Cold War. Look at 1950. 5 of the 12 nations are European. Swap Russia for the USA (yea, we're #3!) - and 5 of the 12 are NATO. None are in Africa. If you throw in Japan - you could argue that 5 of the 12 most populous nations are serious allies of the United States. Freedom's block is at 6.
Today, what are the numbers? Well, we're still #3, but the only European nation is Russia - and they are really an Eurasian power, and not "Western." No one else from NATO is there, and Japan just makes it in. So, that brings us from 5 super-friends to one, and she is getting a bit long in the tooth.
That brings us to 2050. Don't snicker; 2050 is to now what 1976 is to us. Not that far. So, in 2050, how are we doing? We've dropped down to #4 - knocked off by Africa's fast riser Nigeria - and ... we are out of friends.
Time to make some new ones, but the only real candidate that is an auxiliary of both the West and the Anglopshere - India. Brazil? Outside shot at best. Mexico? Not quite, they want the Southwest back.
Other things to ponder: Nigeria, Pakistan, Bangladesh, Ethiopia, Congo - does anyone here see any chance for these nations to grow their economies greater than their population? Without that magic, you will have that toxic mix of poverty and - with the exception of Bangladesh - endemic ethnic conflict.
That doesn't even get in to the incredible demand for resources as basic as food and clean water - not to mention energy and quality of life products. The ecology? Fugetaboutit. Better than average odds that the balance of those nations will wind up making China's ecological nightmare today look like paradise by comparison.
Also note, all of those nations except for Ethiopia and Congo have significant coastlines. Trade, piracy, fisheries, natural resources in EEZ, and so on and so on. Migration? We have yet to see the pressure for migration.
Even if the Western Pacific by mid-century is a lake of eternal peace - the demand for long-dwell, multi-mission naval assets with reach for hard and soft power projection - and the logistics chain to support them - is going to be a keystone to the #3/#4 largest nation - and by then still the largest navy.
Building off that theme - our friend James Holmes over at TheDiplomat has a must read if you just want to run away from the future, A Machiavellian Age of Sea Power;
We cannot shift our burden to another ambitious seafaring power the way Britain, the weary titan, handed off its duties to the United States starting a century ago. Neither China nor India, the most likely candidates, yet possess the capacity or evinces any desire to take up this burden.Oh yes my friends; it has only begun to get interesting out there.
And again, the Maritime Strategy directs us to do all of this at a time when our capacity to found and lead coalitions is on the wane. It’s been said that he who has the gold makes the rules in alliances and coalitions. If the United States has less and less gold — and ships, and manpower — to contribute to preserving freedom of the seas, it will be less able to get its way in coalition circles than in bygone decades.
It is going to get sporty; do try to keep up.