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A uthor: David R. King , Florida State University

When it comes to major U.S. industries, three tends to be the magic number.

Historically, auto manufacturing was long dominated by Chrysler, Ford and General Motors – the so-called “Big Three,” which at one point controlled over 60% of the U.S. auto market. A dominant trio shows up elsewhere, too, in everything from the U.S. defense market – think Lockheed Martin, Boeing and Northrup Grumman – to cellphone service providers (AT&T, T-Mobile and Verizon). The same goes for the U.S. airline industry, in which American, Delta and United fly higher than the rest.

The rule of three also applies to what Americans watch;

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