The Financial Crisis - What Went Wrong?
It all started when the US Federal Reserve circulated far too much money in order to stimulate the economy. Many governments followed suit. Too much money causes "bubbles" in various markets. The American government incurred more debt than any state ever had, and encouraged its citizens to amass more debt than any state had ever done. The banks earned money. It was easy to make money, and those who made less by avoiding risks were idiots.
So the banks took on more and more risk. That's what the politicians wanted, so they would have to help out if things went wrong. The bankers considered themselves absolutely necessary for the system. After all, they were responsible for the building boom. The bankers were guaranteed large salaries, premiums, bonuses, stock options, even when business was bad. If they succeeded, they earned much more. So they gladly took risks.