War will always cause peace in the end no matter how many lives have been taken. If another person such like Hitler rises into power again, How would we stop him? We can't talk to the evil person to just stand down, We would need to start a war to overthrow the government. Look at ISIS, If we let them keep on destroying historical items and killing innocent people then they would turn out to be one of the strongest nations in the world. War will always make peace in the end, No matter the cost of the war or how much lives were taken.
The American Civil War (1861-1865) was the bloodiest war in American history. Many thousands of people died, but after the war ended African Americans were treated much better than before. It still wasn't perfect for the African Americans, but the enslavement and killing of them ended for the most part.
Although past battles have ended on good terms, and led to good things, the fighting never really stops. The problems will never really go away because someone will always be left mad. War causes deaths, and unnecessary money spent. Peace can only be found within ourselves. We just have to chose it. If war caused peace, we wouldn't have been 13+ wars. War might fix short term problems, but in the long it's not going to cause peace.
Initiating force through war can never cause peace. War can only lead to more war. Hate begets hate. That is both true on an individual level and an international one. International politics is complicated, but history has shown us that you can not simultaneously strive for peace and prepare for war.