The reason is simple. If hypothetically speaking, someone had conducted a poll in the US in July '45 (after almost years of hard war in the Pacific) with the si

The reason is simple. If hypothetically speaking, someone had conducted a poll in the US in July '45 (after almost years of hard war in the Pacific) with the single question "are you ok with killing one million Japanese people to save one hundred thousand American boys?", I think the vast majority of the people would have answered yes. America had just lost more than 20000 killed at Iwo Jima and Okinawa, and many more wounded. That's almost exactly the same number as those killed in the whole battle of Normandy (not just on D-day, but during the whole 3 month campaign). Iwo Jima was a tiny speck of land of less than 10 square miles, Okinawa is less than 500 sq miles. For comparison Normandy has an area of more than 10000 square miles. The Japanese were able to draw as much blood while surrendering 500 square miles as the Germans surrendering 20 times as much. Oh, and the Japanese had the kamikazes. I don't think the American's feared the Japanese by this time. After all, in all the battles the casualty ratio was between 1-to-3 and 1-to-10 US vs Japanese casualties. It was a given that they will crush Japan, and it had been so for 2 years already. But war is war, and people die in war. If there was something that could stop the war and save American lives, then Americans wanted it. The alternative to a land invasion was total psychological shock. A few hours after Hiroshima Truman gave his "rain of ruin" speach [1]. He implied that America will drop numerous atomic bombs over Japan (if you pay attention he never says that directly, but it's easy to think he does) We are now prepared to obliterate more rapidly and completely every productive enterprise the Japanese have above ground in any city. We shall destroy their docks, their factories, and their communications. Let there be no mistake; we shall completely destroy Japan's power to make war. It was to spare the Japanese people from utter destruction that the ultimatum of July 26 was issued at Potsdam. Their leaders promptly rejected that ultimatum. If they do not now accept our terms they may expect a rain of ruin from the air, the like of which has never been seen on this earth. Behind this air attack will follow sea and land forces in such numbers and power as they have not yet seen and with the fighting skill of which they are already well aware. Nagasaki was needed because Truman needed to follow through with his threat. [1] https://millercenter.org/the-presidency/presidential-speeches/august-6-1945-statement-president-announcing-use-bomb https://millercenter.org/the-presidency/presidential-speeche...