Check out this page of maps. Fun stuff. My favorite:
No wonder the sun never set on the British Empire. Jeez. Sweden, Belarus, Mongolia, a stan or two, Mail, Chad, Ivory Coast, CAR, Burundi, Rep of Congo, Bolivia, Paraguay, Guatemala, and some micro-European countries did not get invaded by the UK at some point. They didn't like landlocked countries (also on the page of maps), apparently, as that is one of the unifying features of most of these places. Once you rule the waves, I guess you end up trying to rule all the stuff that touches the waves.
Anyhow, check out the various maps and highlight any that you think need some over-thinking.