[mikeash]

CAs aren't geographically limited. Any CA trusted by your computer is trusted for any domain anywhere (with the exception of certificate pinning, which isn't commonly used). That means that a single rogue CA is enough to make HTTPS worthless everywhere.

[bbatsell]

Mozilla actually has done this (sort of), once. They restricted French agency ANSSI's root CA to only be valid for TLDs ending in .fr, .gp, .gf, .mq, .re, .yt, .pm, .bl, .mf, .wf, .pf, .nc, .tf.

https://wiki.mozilla.org/CA:IncludedCAs