The geneva Conventions
The Geneva Conventions were a series of treaties to protect prisoners of war and soldiers. There were four conventions. The first convention (1864) protects the wounded and doctors from attack. The second convention (1906) protects the wounded or shipwrecked navy from attack. The third convention (1929) was made after World War I to protect prisoners of war. During World War I, prisoners were mistreated and tortured for information. The convention says that prisoners are required to give their name and rank and must receive equal treatment. These conventions can be considered "the rules of war."
The turning point
The fourth convention (1949) protects civilians from the inhumane treatment of war. This convention was held after World War II due to America's bombings on Japan. America revolutionized warfare by creating a new conflict in war not discussed in previous conventions. It was a turning point because the citizens are protected from harm which was not a conflict before the bombings.
Justification
The Manhattan Project and the bombings in Japan were justified. The Americans had a "morale advantage" due to the Japanese led them to bomb Japan. The Japanese bombed Hawaii first which led America into the war. Secondly, the Japanese were given opportunities to surrender that were rejected. America's final option was to drop the atomic bombs. The first bomb was not enough so it required two atomic bombs to force Japan to surrender. Japan's honor was to great, so America had no other choice but to bomb the Japanese.