US suddenly looks a “not so good” place to invest because of their huge what are the alternatives ?

Again, what is the alternative to investing in the U.S.? Japan: BOJ isn’t likely to let the yen go past 100. Euroland: most of the politicians were yelping once the dollar hit 1.30 (and apparently European officials have told the Chinese they would not be pleased if China bought more of the Euro).  
So where might be the obvious place for China to invest, which would get the best return? Wouldn’t it be China? But they can’t! Despite highway building, dam making, space programs, they just don’t have the ability to put their money into investments which are better at providing some sort of cash flow in the future than the U.S. Treasuries. And I think once you see *why* they can’t, you end up understanding why the U.S. is the only game in town.  
Here’s another spin: given the demographics in the world – more and more old people – there is no reason why investment return should be positive. Imagine the case where the world contains 10 old people and 1 kid. The 10 need to save for retirement, but they can only invest in the future output of the kid. It’s pretty easy to see – or at least I see it! – that the investment return of the old people will all be negative in real terms – they are using 10 work outputs to buy the one future work output of the kid. Now maybe productivity will increase enough to compensate for the decreasing ratio of workers vs. oldsters. Maybe robots will come to the rescue; the Japanese are taking that route. But other than that, real positive investment returns aren’t a guarantee.  

There aren’t much …. isn’t it ?