While helping all asset categories to rally, the Greenspan put had an undesired consequence: it caused a synchronous one-direction move across asset categories, undermining the effectiveness of asset diversification in lowering market risks.
The bottom line: The resumption of easy money policy by the Federal Reserve in the aftermath of the 2008 financial crisis has re-affirmed and broadened the positive correlation of different asset categories, undermining the effectiveness of asset diversification strategy in reducing market risk.