The Internet connects the world as never before. When you're looking at European websites or chatting with family on vacation in Southeast Asia, it seems like the Internet blankets the entire Earth.
However, the Internet actually relies on a small number of undersea cables to link continents. If they get damaged or cut, it can slow down Internet speed worldwide, or even knock entire countries offline. This happens fairly regularly thanks to accidental collisions with the nets of fishing vessels, anchors of other ships, underwater rocks and even from sharks. However, those incidents usually happen one cable at a time and they're relatively easy to repair; what if someone did it deliberately?
That's the worry of the American military. Recently, Russian submarines and spy ships have spent a lot of time around undersea cables in the Atlantic, North Sea and Asia.
Analysts are worried that in a war situation the Russians will try to cut the cables at extreme depths where it's nearly impossible to repair them. Not only would a major Internet disruption hurt the financial markets, it could hurt communication between the U.S. and its overseas allies at a critical moment.