Central banks have been flooding the economic system with easy money for decades. This has enriched the upper class and created bubbles in assets such as equities and real estate, writes Julian Zelizer. In the process, it has impoverished the middle class and the poor, says Zelizer. Central banks are trying to tame this increase in price levels by raising interest rates,. But a rise in interest rates threatens to collapse the House of Cards on which so much of the economy is built," he adds.