Collective plunge. Due to the tight liquidity and unprecedented tension in the credit market, all investment markets are under pressure to sell assets, and the direct reflection of the commodity futures market is the collective plunge. The subprime mortgage crisis is that American financial institutions lend a large number of loans to people with poor credit and insufficient repayment ability, which eventually leads to the failure of financial institutions to recover loans as agreed, resulting in insufficient cash liquidity of US dollars.