SAN FRANCISCO  The era of the American Internet is ending.

Invented by American computer scientists during the 1970s, the Internet has been embraced around the globe. During the network’s first three decades, most Internet traffic flowed through the United States. In many cases, data sent between two locations within a given country also passed through the United States.

Engineers who help run the Internet said that it would have been impossible for the United States to maintain its hegemony over the long run because of the very nature of the Internet; it has no central point of control.

And now, the balance of power is shifting. Data is increasingly flowing around the United States, which may have intelligence  and conceivably military  consequences.

American intelligence officials have warned about this shift. “Because of the nature of global telecommunications, we are playing with a tremendous home-field advantage, and we need to exploit that edge,” Michael V. Hayden, the director of the Central Intelligence Agency, testified before the Senate Judiciary Committee in 2006. “We also need to protect that edge, and we need to protect those who provide it to us.”