LONDON -- The saga of Edward Snowden and the NSA makes one thing clear: The United States' central role in developing the Internet and hosting its most powerful players has made it the global leader in the surveillance game.

Other countries, from dictatorships to democracies, are also avid snoopers, tapping into the high-capacity fiber optic cables to intercept Internet traffic, scooping their citizens' data off domestic servers, and launching cyberattacks to access foreign networks.

But experts in the field say that Silicon Valley has made America a surveillance superpower, allowing its spies access to massive mountains of data being collected by the world's leading communications, social media, and online storage companies.

That's on top of the United States' fiber optic infrastructure -- responsible for just under a third of the world's international Internet capacity, according to telecom research firm TeleGeography -- which allows it to act as a global postmaster, complete with the ability to peek at a big chunk of the world's messages in transit.

"The sheer power of the U.S. infrastructure is that quite often data would be routed though the U.S. even if it didn't make geographical sense," said Joss Wright, a researcher with the Oxford Internet Institute. "The current status quo is a huge benefit to the U.S."

The status quo is particularly favorable to America because online spying drills into people's private everyday lives in a way that other, more traditional forms of espionage can't match. So countries such as Italy, where a culture of rampant wiretapping means that authorities regularly eavesdrop on private conversations, can't match the level of detail drawn from Internet searches or email traffic analysis.

"It's as bad as reading your diary," Wright said. Then he corrected himself: "It's far worse than reading your diary. Because you don't write everything in your diary."

Although the details of how the NSA's PRISM program draws its data from these firms remain shrouded in secrecy, documents leaked by spy agency systems analyst Snowden said its inside track with U.S. tech firms afforded "one of the most valuable, unique, and productive" avenues for intelligence-gathering. How much cooperation America's Internet giants are giving the government in this inside track relationship is a key unanswered question.

And the pool of information in American hands is vast. Redmond, Wash.-based Microsoft Corp.'s Internet Explorer accounts for between a quarter and half of all browsers, according to various estimates. Mountain View, Calif.-based Google Inc. carries two-thirds of the world's online search traffic, analysts say. Menlo Park, Calif.-based Facebook Inc. has some 900 million users -- a figure that accounts for a third of the world's estimated 2.7 billion Internet-goers.

Electronic eavesdropping is far from an exclusively American pursuit. China and Russia have long hosted intrusive surveillance regimes. Russia's "SORM," the Russian-language acronym for System for Operational-Investigative Activities, allows officials to directly access nearly every Internet service provider in the country.

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In China, surveillance is "pervasive, extensive, but perhaps not as high-tech" as in the United States, said Andrew Lih, a professor of journalism at American University in Washington. He said major Internet players such as microblogging service Sina, chat service QQ, or Chinese search giant Baidu were required to have staff -- perhaps as many as several hundred people -- specially tasked with carrying out the state's bidding, from surveillance to censorship.