The United States' Diplomatic Dilemma

In class today we briefly touched upon the sixth principle of jus ad bellem, war is the last resort after all diplomatic solutions are exhausted, and we also mentioned how the United States did not exhaust this avenue during World War II because the leadership "did not talk to or associate with evil." This was very true for the first portion of the war, when the world powers had the ability to place economic and other types of sanctions on Germany. Thus, the German superpower would have to rely on itself for its materials and therefore would not be able to flourish as it had. One such sanction could have been on a restriction to sell oil and gasoline to Germany because their armed forces heavily relied on these things to be mobile. However, this is a little off topic because I think that there was a point very soon after the war had begun when the diplomatic solutions no longer mattered and that point was when the world discovered the killing of millions of Jews, Polish, etc. by Nazi Germany. Once Germany decided to kill people by the millions in the concentration camps is when Hitler gave up his rights to diplomacy because the United States and other global powers had the right to protect those millions of people being slaughtered. From an ethical standpoint, this act of self defense for all humanity greatly outweighs the need for diplomacy because people's life and liberty, two extremely important ethical claims, were being stampeded. Therefore, I think that too much diplomacy occurred during World War II on the side of the United States and the neutrality principles practiced by the United States were unethical based on the ongoing suffering of millions in Hitler's concentration camps.