The Geneva Conventions comprise four treaties and three additional protocols that set the standards in international law for humanitarian treatment of the victims of war. The first three were ratified in Geneva, Switzerland in 1864, 1906, and 1929. The singular term Geneva Convention refers to the agreements of 1949, negotiated in the aftermath of World War II, updating the terms of the first three treaties and adding a fourth treaty. The language is extensive, with articles defining the basic rights of those captured during a military conflict, establishing protections for the wounded, and addressing protections for civilians in and around a war zone.
Japan never signed the Geneva Conventions. This allowed its military to show aggressive and inhumane treatment of soldiers, Prisoners of War, and civilians alike, especially during the Second Sino-Japanese War. Their brutality was mainly driven by their native, imperialistic ideology of war.
During Japan's takeover of Hawaii, the Japanese barred no holds in harming Red Cross medics. During the occupation, the Japanese military severely punished the civilian population if they disobeyed Japanese rule, for example if they didn't bow to passing soldiers. In one incident, an elementary school principal named Mr. Murphy was executed via decapitation for secretly keeping a forbidden radio. Furthermore, American POWs were treated badly, as the Japanese were contemptuous of the ideas of surrender and taking prisoner. They forced the POWs to build defenses and repairing damages caused during the invasion. These labors were specifically used in working the POWs to death.
By the time of Hawaii's liberation, American troops from the mainland were shocked and horrified of the Japanese's brutality that they were willingly to kill any Japanese soldiers and personnel in retribution.
Some 30 years after the Change, the Geneva Convention was just one more relic from a bygone age. In war you did what you could get away with. However, armies still often refrained from murdering POWs, more from a fear of retaliation than from any respect for the old document.