EdT-The better question might be, how many countries haven't? Every empire (including the ones that preferred to call themselves democracies or people's republics) has felt the need to convert, displace, or just plain exterminate people who had the bad luck to have gotten there first.(we like to use terms like "indigenous" or "aboriginal", but the truth is that humans are migratory by nature)

The last hundred or so years have been particularly bad--in the 20th Century, democide, which has been roughly defined as "murder by your own government"(and a term created because "genocide" was too restrictive) surpassed war as the leading cause of unnatural death. And the numbers aren't even close--there is a new name for murderous gov'ts-mortocracies, and they are classified by the numbers they have killed-

Megamurders are those gov'ts that have killed a million or more, and include Japan, Cambodia, Ottoman Turkey, Vietnam, Poland, Pakistan, North Korea, Mexico, and Tsarist Russia

Deka-Megamurderers are gov'ts that have killed ten million or more, and include the big ones that we all know--People's Republic of China, USSR, Nazi Germany(a bit of a surprise that they only rank third), and a dark horse, the Kuomintang Republic of China(at least for those of us who forgot that Chiang-Kai-Shek committed the single most horrific act in human history when, on July 9th, 1938, he blew up the dike at Huayauankou on the south bank of the Yellow River, flooding 21,000 square miles, killing more than a million of his own people, and leaving 12 million homeless)

Cento-kilo murderers(100,000 or more, and who are an anticlimax, compared to the above) Include Attaturk's Turkey, the UK, Portugal, Rwanda and Indonesia.

In addition to these deaths, one of the better kept secrets concerning "The Good War" is that between 500,000 and 2 million ethnic Germans died between 1944-1950 as the result of displacement, evacuation and expulsion, much of which was related to the redefinition of borders in the Pottsdam Agreement.

Though the US, in this time period, at least, didn't murder enough of it's own to make the list (like it did in the 19th century), it certainly was a party to some of the above--and don't mention the wars...