For nearly half a century, global finance operated on a remarkably stable arrangement: the United States spent more than it earned, ran persistent deficits, and the rest of the world helped finance those gaps by purchasing American debt. Two countries stood at the center of that equation — China and Japan. Now, both appear to be stepping back. China’s holdings of US Treasuries have fallen to around $693 billion, the lowest level since 2007. At one point, Beijing held nearly $1.3 trillion in US government debt, making it one of Washington’s largest creditors. Japanese investors, meanwhile, have accelerated Treasury sales at one of the fastest rates seen in years. [...]