If what you’re asking is “could the US hypothetically cut off the Internet in a worst case scenario”, like a war or something, the answer is “sure”. If the US were bent on destroying Internet infrastructure – submarine cable interchange stations, satellite uplink stations, major international cables, whatever, all of those are not hardened not realistically protectable targets and could be physically destroyed. Taking out communications infrastructure was our first target in the Gulf War.

That’s probably also be true of a number of major military powers, but I’d be particularly confident of the US’s ability to knock out communications.

I was reading an article from a retired Navy officer a while back where he was talking about how submarine cables were vulnerable, and he pointed out that in past wars, we’ve destroyed them, and should also assume that an opponent would do the same.