Ryujin
Legend
Unless need drives them to do so.
One can imagine, for example, that, in the near future, the world will need far more unified policies on resource use, under which individual nations simply could not be allowed to forge their own paths.
Yes, for example water is already becoming an issue. California is having a fairly hard time of it (that'll teach 'em for building their largest city in a desert) and on more than one occasion, in the past, there's been talk of pipelining water down from the Canadian border to there. The Great Lakes are another sticking point.