I think it would be possible to sabotage the Internet via the fiber optic backbone.
During the Vietnam War there was a significant mathematical analysis devoted to “breaking networks” by removing the smallest possible number of strategically placed links. Rand Corporation performed such studies and developed (and published) the “Max Flow Min Cut Theorem.” I think it may have been intended to determine where to bomb the Ho Chi Minh Trail—bridges and so on.
Anyway, if someone had a full Fiber Optic map (not easy to come by, by the way) it would be possible to determine points of attack to take down not only the Internet but telephone and cellular service as well. They all travel the fiber optic backbone.
An this is without necessarily even touching the big hubs for switching and cross-connection located in a number of major cities.
If you’ve got a general area/pathways (and there are some fairly straightforward routings) you can mark locations for state underground service alert and they’ll come out and mark the spot exactly so you won’t hit it while excavating...