Are Facebook and Google the New Monopolies?

The rise of global technology superstars like Amazon, Apple, Facebook and Google are creating new challenges for competition watchdogs. Along with Microsoft Corp., they are the five most valuable companies in the U.S. today, a ranking that only included Microsoft 10 years ago. They dominate their markets, from e-books and smart phones to search advertising and social-media traffic on mobile devices. This is fueling a global debate over whether it's time to rein in such winner-take-all companies.