"Claims that various policies or phenomena—such as low interest rates in the early 2000s or financial flows from abroad—were responsible for the growth of the housing bubble, do not adequately explain either the bubble or the destruction that occurred when the bubble deflated. The U.S. has had housing bubbles in the past—most recently in the late 1970s and late 1980s—but when these bubbles deflated they did not cause a financial crisis. Similarly, other developed countries experienced housing bubbles in the 2000s, some even larger than the U.S. bubble, but when their bubbles deflated the housing losses were small. Only in the U.S. did the deflation of the most recent housing bubble cause a financial meltdown and a serious financial crisis. The reason for this is that only in the U.S. did subprime and other risky loans constitute half of all outstanding mortgages when the bubble deflated. It wasn’t the size of the bubble that was the key; it was its content."