One glance at the distribution of wealth around the world and the shift is obvious: financial power, so long concentrated in the developed economies, is dispersing. Oil-rich countries and Asian central banks are now among the world’s largest sources of capital. What’s more, the influx of liquidity these players have brought is enabling hedge funds and private-equity firms to soar in the pecking order of financial intermediation.

New research from the McKinsey Global Institute shows that the assets of these four groups of investors—the new power brokers—have nearly tripled since 2000, reaching roughly $8.5 trillion at the end of 2006 (Exhibit 1).¹ This sum is equivalent to about 5 percent of total global financial assets ($167 trillion) at the end of 2006, an impressive number for players that lay on the fringes of global financial markets just five years ago.

The impact and visibility of this quartet exceed its relative size, despite the discreet way its members operate. Among other things, they have helped lower the cost of capital for borrowers around the world. In the United States, we estimate, long-term interest rates are as...