Britain has invaded all but 22 countries Nov 16 2012
Of the current 200 nations in the world, the British have invaded all but 22 of them. The lucky 22 include Sweden, Luxembourg, Mongolia, Bolivia, and Belarus. The full analysis is available in Laycock's book, All the Countries We've Ever Invaded.
Stuart Laycock, the author, has worked his way around the globe, through each country alphabetically, researching its history to establish whether, at any point, they have experienced an incursion by Britain.
Only a comparatively small proportion of the total in Mr Laycock's list of invaded states actually formed an official part of the empire.
The remainder have been included because the British were found to have achieved some sort of military presence in the territory -- however transitory -- either through force, the threat of force, negotiation or payment.
Incursions by British pirates, privateers or armed explorers have also been included, provided they were operating with the approval of their government.
The US currently has military personnel stationed in all but 43 countries.
For instance, as of Sept. 30, 2011, there were 53,766 military personnel in Germany, 39,222 in Japan, 10,801 in Italy and 9,382 in the United Kingdom. That makes sense. But wait, scanning the list, you also see nine troops in Mali, eight in Barbados, seven in Laos, six in Lithuania, five in Lebanon, four in Moldova, three in Mongolia, two in Suriname and one in Gabon.
But the presence in most of those countries is due to diplomatic usage of military personnel. (thx, aaron)