Technology giants like Google and Facebook are expanding efforts to control more of the world’s Internet backbone, raising tensions with telecom companies over who runs the Web. In the past year, these companies that supply much of the world’s online content have ramped up their investment in Internet infrastructure. The moves include bringing online new submarine and underground cables they have funded, striking long-term agreements to lease so-called dark fiber, and building their own networking hardware. In the process, they are beginning to rival some of the telecom companies that count them as clients. Google has spent years piecing together a network of private fiber-optic cables and now controls more than 100,000 miles of routes around the world, said one person familiar with its assets. That is bigger than the size of the continental U.S. network run by Sprint, which covers less than 40,000 miles.