[zupreme]

Have you considered ICANN? Or USA-based DNS providers?

One letter, from the right agency, can do a great deal.

[emteycz]

I don't think turning off DNS servers is 1) actually possible (people would start running mirrors + other countries continue to run) and 2) would disable the internet into uselessness (anything IP based still works).

[int_19h]

It doesn't have to be 100% effective, just as with the Great Firewall. Shutting down DNS would shut down most existing apps until they're updated (and also the app stores that are normally used to update them), and preclude the majority from accessing anything online.