Japanese war crimes
The U.S. officially classified all 3,649 military and civilian casualties and destruction of military property at Pearl Harbor as non-combatants as there was no state of war between the U.S. and Japan when the attack occurred. Joseph B. Keenan, the chief prosecutor in the Tokyo Trials, says that the attack on Pearl Harbor not only happened without a declaration of war but was also a treacherous and deceitful act. In fact, Japan and the U.S. were still negotiating for a possible peace agreement which kept U.S. officials very distracted when Japanese planes bombed Pearl Harbor. Keenan explained the definition of a war of aggression and the criminality of the attack on Pearl Harbor:
Nuclear warfare
In late June 1945, as the U.S. wrapped up the two-and-a-half-month Battle of Okinawa (which cost the lives of 260,000 people, including 150,000 civilians), it was faced with the prospect of invading the Japanese home islands in an operation codenamed Operation Downfall. Based on the U.S. casualties from the preceding island-hopping campaigns, American commanders estimated that between 50,000 and 500,000 U.S. troops would die and at least 600,000–1,000,000 others would be injured while invading the Japanese home islands. The U.S. manufacture of 500,000 Purple Hearts from the anticipated high level of casualties during the U.S. invasion of Japan gave a demonstration of how deadly and costly it would be. President Harry S. Truman realized he could not afford such a horrendous casualty rate, especially since over 400,000 American combatants had already died fighting in both the European and the Pacific theaters of the war.