The data cables of the Mediterranean. (Image: TeleGeography)
Why the Mediterranean is the Achilles’ heel of the web:

Internet users in the Middle East and India might be glad to see the back of 2008 – it was bookended by cable breaks under the Mediterranean Sea that disrupted access across the region.
…
Undersea data cables are, in fact, surprisingly delicate. Most are just a fraction of an inch thick and more than 50 Atlantic cables alone were severed or damaged in 2007, according to Global Marine Systems, a firm that repairs marine cables.

I find the political issue the most interesting: could countries, or whole continents, decide one day to close up shop and isolate themselves from the rest of the world’s data? Is this even possible? Could the EU exist without external data? How about Iran? China made a go of this and even with the Great Firewall, data is crossing borders.
This event is unlikely, but might occur if third-parties act to isolate regions or countries.