http://arstechnica.com/security/2015/09/gchq-tried-to-track-web-visits-of-every-visible-user-on-internet/
http://www.theregister.co.uk/2015/09/25/gchq_tracked_web_browsing_habits_karma_police/
I have assumed that for more than a decade every intel agency in the world was attempting to do this.
The only practical limitation to the practice is budget. So Zimbabwe is probably not playing the game, but several nations in NATO probably are, as are China and Russia. The Norks are probably prepared to starve a few million of their own in order to get a seat at the table. Japan? Why not?
But the US is the big winner because it basically *is* the internet - both its creator and its infrastructure. Here's a map of the internet backbone. It's a couple years out of date, but that shouldn't matter much, as it has always looked more or less like this:
(https://2.bp.blogspot.com/-6jOm6WKb1Hg/T8g_3_SSFhI/AAAAAAAAACQ/FGVT3R9IFKw/s1600/global-traffic-map-large.png)