Who Are America’s Wealthiest People? Small- and medium-sized businesses are the engines that drive the American economy. An IRS study of everyone who died with a net worth of at least $600,000 (and thus was required to file an estate tax return) showed America’s wealthiest citizens all have one thing in common: they all held significant blocks of stock in closely held private companies.  In a nutshell, the surest way to get rich in America is to own a business. Want to know the actual numbers?   According to  IRS reports, over six million businesses file tax returns each year: 80…