The concept of war is since centuries. The biggest war fought in India was the war of Mahabharata- a war with advanced weapon and technologies. The war was between Pandavas and Kauravas- a fight between good and evil, justice and injustice. Krishna played an important role in the fight of Mahabharat. He encouraged Arjuna to fight for Dharma. While Arjuna cried that he would be unable to kill his family members, Krishna said that Arjuna must understand that no one can kill anyone. There is no concept of dying and killing and if anyone think so,it is their sheer ignorance. Here Krishna wants t say that a soul never dies and if Arjuna thinks that he is killing someone than he is wrong. Arjuna or no one can kill anyone as soul never dies.
What was Krishna actually?
Many devotees are always afraid to accept Krishna fully. Few accepted the childhood of Krishna, few accepted his youth. Surdas who created beautiful hymns for Krishna accepted his childhood for creating hymns. While Krishna danced with many women, he played flute, Surdas pierced his eyes with needle and he blinded himself so that he could not fall in love with women. While another devotee, Keshavdas accepted the youth of Krishna, his dance with women, playing flute etc.
On the other side, Mahatma Gandhi was a stern believer of non violence and it was very difficult for him to accept that Krishna can lead the war. So for his own convenience, he mentioned that mahabharata is a metaphor and the act of war was the victory of good over evil. But how we can conclude that all good people were in Pandavas side while all bad in Kauravas side. Bhishma was in Kauravas side though he was a good man. Likewise, there will be bad people in Pandavas side too. There was always a little Rama in Ravana and little Ravana in Rama. No one is completely pure. These are all dualities of life.
Krishna supported the war and lead a life with no grief. He lead a life in totality by accepting the duality of life. Though his one feet was in peace, the other feet had the courage to fight. He had the courage to accept the curse of Kunti when all Kauravas died. There is always a proportion of good and evil in life and Krishna had the ability to understand the life. Krishna is the only incarnation who lived his life fully. But are we able to accept him totally?
Reference: Krishna- the man and his philosophy by Osho.