out, he was killed by the USAAF in Operation Vengeance in 1943. At the Tokyo Trials, Prime Minister Hideki Tojo, Shigenori Tōgō, then Foreign Minister, Shigetarō Shimada, the Minister of the Navy, and Osami Nagano, Chief of Naval General Staff, were charged with crimes against peace (charges 1 to 36) and murder (charges 37 to 52) in connection with the attack on Pearl Harbor. Along with war crimes and crimes against humanity (charges 53 to 55), Tojo was among the seven Japanese leaders sentenced to death and executed by hanging in 1948, Shigenori Tōgō received a 20-year sentence, Shimada received a life sentence, and Nagano died of natural causes during the Trial in 1947. Over the years, many Japanese nationalists argued that the attack on Pearl Harbor was justified as an act of self-defense in response to the oil embargo imposed by the United States. Most historians and scholars agree that the oil embargo cannot be used as justification for using military force against a foreign nation imposing the embargo because there is a clear distinction between a perception of something being essential to the welfare of the nation-state and a threat sufficiently serious to warrant an act of force in response, which Japan had failed to consider. Japanese scholar and diplomat Takeo Iguchi states that it is "[h]ard to say from the perspective of international law that exercising the right of self-defense against economic pressures is considered valid." While Japan felt that its dreams of further expansion would be brought to a halt by the American embargo, this "need" cannot be considered proportional with the destruction suffered by the U.S. Pacific Fleet at Pearl Harbor, intended by Japanese military planners to be as devastating as possible. Mass killings The estimated number of people killed by Japanese troops vary. R. J. Rummel, a professor of political science at the University of Hawaii, estimates that between 1937 and 1945, the Japanese military murdered from nearly three to over ten million people, most likely six million Chinese, Indians, Koreans, Malaysians, Indonesians, Filipinos and Indochinese, among others, including European, American and Australian prisoners of war. According to Rummel, "This democide [i.e., death by government] was due to a morally bankrupt political and military strategy, military expediency and custom, and national culture." According to Rummel, in China alone, from 1937 to 1945, approximately 3.9 million Chinese were killed, mostly civilians, as a direct result