Can anybody explain me easily what is housing bubble and how it cause financial crisis?
A bubble is when the price of a speculative asset becomes unreasonably high. If we are talking about the housing market this means the price of real estate. When the bubble bursts the price comes crashing down and people are left with assets that are now worth much less than what they paid for them. A major reason the housing bubble was so bad was because of the widespread practice of giving subprime mortgages, meaning giving mortgages to people who did not have the credentials to be qualified for a good mortgage, so they were given mortgages at very high interest rates. The big investment banks then invested in subprime mortgages through various complicated investment products. When the bubble burst and subprime mortgages started to be defaulted on these big investment banks were left with worthless assets and took huge losses.