Where the billionaires come from
The Forbes 400 list of richest Americans (1 billion or more) can be broken down by category.
Of all these wealthy people, only a third made their money in finance, investment, and real estate. The rest were selling goods or services. One exception is Michael Bloomberg, the only one listed under "politics."
278 of them are self-made. Obviously, there's overlap with the other categories.
Their combined net worth--not salaries or income, net worth--is about $1.37 trillion. Enough to pay--once--a single year's current Federal deficit.