It is incredibly unlikely that China would ever call in its debts as any damage done to the dollar would be fairly insignificant compared to the impact on China’s own economy and currency.  America can afford to service its debts and doing so is a major stimulus to the global economy. Nobody has an interest in breaking the dollar, as doing so would cause a run on every bank in the world – including the Bank of China. China holds reserves roughly equivalent to M1 – cash in circulation in the US (although it’s worth nothing this represents about four percent of the actual dollars in the world) and so a massive release of dollar-denominated assets would hurt the dollar greatly. The results would see the price of oil, and most other commodities, skyrocket as they are priced in dollars and would bring the entire global financial system to a halt. China has no interest in either of these things happening.