Did Rukmini say anything to Lord Krishna before Mahabharata begin? Lord Krishna totally supported the war and he wanted to be on Pandava's side. Did Rukmini supported these all decisions?
Is there any role of Rukmini behind Mahabharata war?
There is no source mentioned in Rukmani supporting Lord Krishna or saying anything important or specific about Mahabharat to Lord Krishna. As far as Lord Krishna supporting a war is concerned, Lord Krishna knew that war always causes destruction of life and many other resources, so saying this he supported this war isn't right. Lord Krishna went as shanti doot to hastinapur and presented proposals so that peaceful solution can be found to which Duryodhana refused.
However this war was the only option left to establish Dharma, Hence Mahabharat took place and Lord Krishna did what was necessary and was to be done.