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 even launching cyberattacks to win access to 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 the telecommunications 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,” Joss Wright, a researcher with the Oxford Internet Institute, said in a telephone interview. “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 like 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 Edward Snowden to the Guardian and The Washington Post newspapers 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.

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

Electronic eavesdropping is, of course, far from an exclusively American pursuit. Many other nations pry further and with less oversight.

China and Russia have long hosted intrusive surveillance regimes. Russia’s “SORM,” the Russian-language acronym for System for Operational-Investigative Activities, allows government officials to directly access nearly every Internet service provider in the country.

Initially set up to allow the FSB, the successor organization to the KGB, unfettered access to Russia’s Internet traffic, the scope of SORM has grown dramatically since Vladimir Putin took power in 2000 and now allows a wide range law enforcement agencies to monitor Russians’ messages.

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 there were required to have staff specially tasked with carrying out the state’s bidding, from surveillance to censorship.

What sets America apart is that it sits at the center of gravity for much of world’s social media, communications, and online storage.

Americans’ “position in the network, the range of services that they offer globally, the size of their infrastructure, and the amount of bandwidth means that the U.S. is in a very privileged position to surveil internationally,” said Wright.

Even in the dark arts of cyberespionage, America seems to have mastered the field. The FBI has been targeting criminals with sophisticated surveillance software for years, while one U.S. general recently boasted of hacking his enemies in Afghanistan.