The "Saipan Ratio":
After the Japanese attack failed, General Saito and Admiral Chuichi Nagumo committed suicide, joining in death nearly all of the island’s 30,000 Japanese defenders. U.S. casualties were also heavy: 2,949 killed in action and 10,364 wounded (about 20 percent of the American invasion force). The high number of American casualties at Saipan relative to those inflicted on the Japanese defenders (known as the “Saipan ratio”) shocked the U.S. Joint Chiefs of Staff (JCS). An August 1944 JCS report ominously noted: “On this basis it might cost us half a million American lives and many times that number wounded … in the [Japanese] home islands.” Saito’s defense of Saipan failed, but the Americans’ bloody combat experience there, and later at Iwo Jima and Okinawa in 1945, inexorably led to the United States’ fateful decision to use atomic bombs to end the Pacific War. (See D.M. Giangreco’s acclaimed book Hell to Pay, Naval Institute Press, 2009.)
Iwo Jima: US Casualties: 6,821 killed 19,217 wounded (26,038 total) Japanese: 17,845–18,375 dead, over 3000 missing, 216 captured (20,530–21,060 troops total so 20,314-20,744 killed) Making the "Iwo Jima Ratio": roughly 4:1 or somewhere between 1.25-1.28-1 including wounded.
Okinawa: US 20,195 dead, 55,162 wounded (75,357 total). Japanese: ~96,000 killed with another 7,000 captured. The "Okinawa Ratio" was roughly 5:1 or 1.27:1 including wounded. (another 40,000-150,000 Okinawan civilians killed out a population of roughly 300,000 or roughly 13%-50%)
Given that the US expected that 3.5 Million Japanese troops were be available to defend the Home Islands, the decision to drop the Atomic Bombs was a no-brainer. After Okinawa, the US Military signed a contract for 1 million Purple Heart medals for the Invasions of the Home Islands. Only 500,00 were made before the war ended. Those medals are still the ones being handed out through Korea, Vietnam, Iraq, and now in Afghanistan.
What does that have to do with North Korea ??
The Norks are more fervently devoted to the Kims then the Japanese were to the Emperor. Every single ones would rather die/be killed then surrender to the RoK's or US soldiers. And they will try to take as many ROKs or Americans with them as possible.
And there are ~25.4 million Norks. Seoul is less then 30 miles from the DMZ and the Norks have thousands of tube and missile artillery pieces that can hit Seoul and it's 10.3 million people. Even if we did take out Kim and much of his missile capability, it will be a bloodbath on par with civilian causalities on Okinawa, Hiroshima, Nagasaki, and the Firebombing of Tokyo, combined.
Which is why I truly hope that the Chinese will do the Decapitate and Disarm strike and put someone they can control a little better on the "throne", and leave us the ROK the hell out of it...
eta: cleaned up spelling errors and some cut and paste errors