Over the last decade, these countries’ foreign-exchange reserves have swelled from $750 billion to $6.3 trillion – more than 50% of the global total – providing a major source of financing that has effectively suppressed long-term US borrowing costs. With yields on US ten-year bonds falling by 45% annually, on average, from 2000 to 2012, the US was able to finance its debt on exceptionally favorable terms.