According to the Telegraph, that would be Britain.
Every [British] schoolboy used to know that at the height of the empire, almost a quarter of the atlas was coloured pink, showing the extent of British rule.
But that oft recited fact dramatically understates the remarkable global reach achieved by this country.
A new study has found that at various times the British have invaded almost 90 per cent of the countries around the globe.
The analysis of the histories of the almost 200 countries in the world found only 22 which have never experienced an invasion by the British.
. . .
The analysis is contained in a new book, All the Countries We've Ever Invaded: And the Few We Never Got Round To.
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.
So, many countries which once formed part of the Spanish empire and seem to have little historical connection with the UK, such as Costa Rica, Ecuador and El Salvador, make the list because of the repeated raids they suffered from state-sanctioned British sailors.
. . .
The only other nation which has achieved anything approaching the British total, Mr Laycock said, is France – which also holds the unfortunate record for having endured the most British invasions.
There's more at the link, including a list of the 22 fortunate nations that have unaccountably escaped England's invasive tendencies - thus far, at any rate . . .
The report reminds me of a joke that circulated in South Africa several decades ago.
Q: Why do people say that 'the sun never sets on the British Empire'?
A: Because God would never trust an Englishman in the dark!