The Japanese chased the Chinese Army 6000 miles in the '30s and were never able to pin them down to a fight of one on one, that the Japanese were sure to win. So the Japanese tried to "lure the tiger out of the mountains" by killing so many millions in the city. The Chinese were not drawn out to defend their cities because they knew if 5 million had to die for China to not be taken, then that was the way it would be.
Same thing when Sir Winston failed to save Coventon, UK because it would have tipped the Germans to their code must have been broke.
War is hell, and the leaders must make sometimes brutal decisions.