The Killing Fields - Over 2 million out of a population of 5 million. Don't even have to look that one up.
Next door:
http://wn.com/operation_montagnard
http://www.youtube.com/watch?feature=player_embedded&v=e2y5Ko9lzYk#t=153s

Over 1 million in this genocide.

Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good ...