The population of millionaires worldwide surged by 9 percent last year, growing to 12 million, according to a report.
The World Wealth Report, from Capgemini and RBC Wealth Management, said rising stock markets and stronger real estate helped create 1 million new millionaires worldwide. Their wealth surged 10 percent to $46 trillion—more than the combined gross domestic product of the European Union, the U.S., China and Japan. (The report defined millionaires as individuals with $1 million or more in investable assets.)
"Overall, we saw strong equities, stronger real estate markets, and a bottoming out of the economies in the developed markets," said William Sullivan, global head of financial services for Capgemini. "All of those factors were able to drive growth."
The report also highlighted the strength of U.S. wealth creation relative to the rest of the world, especially emerging markets. North America reclaimed its position in 2012 as the region with the most millionaires—a year after Asia took over the top spot for the first time.
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Capgemini said it expects the switch is temporary and Asia will regain its top spot in the next year or two. Still, Sullivan said, weakness in Asia—especially China—has led many companies to revise down their previous forecasts for wealth creation for the region.
"I think it's been tempered a little," he said. "It may not be the astronomical growth predicted." Still, he said the domestic markets in Asia are so strong that the region will see strong millionaire growth in the coming years.
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The world's millionaires remain fairly cautious when it comes to investing. U.S. millionaires have one fifth of their investments in cash, while Japanese millionaires have half of their portfolio in cash, Sullivan said.
In North America, about a third of millionaires are focused on wealth preservation, while 28 percent were focused on growing their wealth.
—By CNBC's Robert Frank. Follow him on Twitter @robtfrank.