China is in a trading relationship with America. Due to China rapid expansion, it was able to make a lot of sales to the US, but the payment for this sales are been lend to the US, this greatly increase the amount of money that the US is owning China and make it extremely difficult for US to pay up. So obviously the debts have to be written off, because without that been done, the US will not be able to afford goods offer by China. This places a major strain on China's economy.
