You've got it the wrong way around.
The idea of winning a war by way of killing so many of the opposition that the rest will surrender or retreat is viable some of the time, but horrific. And truth be told, it doesn't work nearly as well in real life as it does on paper; people are unpredictable creatures at the best of times, and there are plenty of cases of soldiers or entire armies fighting to the very last, horrific fate be damned, rather than surrender. In particular populations and politicians may fall prey to the sunk cost fallacy i.e. "We've already lost N soldier fighting this war, we can't give up now, else they died for nothing." You can't expect to win a war if you assume your opponents are rational actors who prioritize self preservation, because that isn't always going to be the case.
The right way to do it, and in fact the way that's had a better track record of making wars end, is to destroy the ability of the enemy to make war altogether. For a protracted conflict, you get more bang for your buck destroying logistic, communication and supply capability than you do killing enemy soldiers in a fair fight. Any modern national military is only as capable of making war as they are capable of supplying, commanding and reinforcing their armed forces. Obviously this doesn't work in a guerrilla engagement, where supply lines may be nonexistent, or against a foe who hides among civilians. Iraq is a good example of where this strategy does and doesn't work; the official conflict ended rapidly, with the army defeated in short order (and without massive casualties; many Iraqi soldiers never even saw action), but the same approach cannot be used to maintain an occupation.
For a hypothetical conflict between two nations armed with robots, this form of conflict is even more likely; infantry forces require less logistical support than drone forces. In order to win, you don't grind your enemy's robotic forces into dust in a fair fight and you don't try to terrorize their populace into surrendering; instead you destroy their communications so they can't send in the drones, you destroy their factories, airbases, munitions dumps and whatever else they need to build and maintain their robotic fleet and you prevent them from doing the same thing to you. You don't have much chance of occupying a country with a robotic army any more than you can occupy a country with tanks, aircraft or warships; occupation pretty much requires men on the ground. This does mean that a robot armed nation might win a conflict without casualties, but must be prepared to suffer losses if they plan on conquering rather than letting their foe surrender and retain their own government.