Often in war, there are logistical issues about holding territory and governing the captured, but how often in history has the conquering country simply killed everyone (though presumably, given the nature of history, the women of child-bearing age would probably all be enslaved) and left the entire land that they took barren? I’m not talking about cutting a swath through a country to some strategic goal, but the systematic destruction of an entire national country so that the conquerors didn’t have to deal with annoying questions about converting the captured or holding on to land.
I’m guessing not much, given how valuable slaves to work your underground sugar mines are, and probably if we limit the area to a small country or a city-state, it has happened much more often than an entire country. Is it too hard to do? Too valuable to kill off millions of free slave labor? Surely it couldn’t be that people wouldn’t cross that line, plenty of crazed maniacs fanatical enough to wipe out a country of tens of millions of people if given the chance litter the history books