The Pandavas were the sons of Kunti, Shri Krishna's aunt. When Dushasana tried to disrobe Draupadi in the crowded royal court, Draupadi called out to Shri Krishna with all her heart. The Lord made her sari endless and protected her honour.
To avoid war, Shri Krishna went to Hastinapur as a messenger of peace and asked for just five villages for the Pandavas. Duryodhana refused to give even as much land as would fit on the point of a needle, and tried to take Shri Krishna prisoner. Then the Lord revealed his immense cosmic form.
At Kurukshetra, Shri Krishna promised not to take up arms and agreed to be Arjuna's charioteer. Before the battle began, Arjuna saw his own relatives facing him, was overcome with doubt and sorrow, and laid down his bow.
Then Shri Krishna gave Arjuna the teaching of the Bhagavad Gita: the soul is eternal, and a person has a right only to their actions, never to their fruits ("Karmanye vadhikaraste ma phaleshu kadachana"). He explained the paths of action, knowledge and devotion (Karma Yoga, Jnana Yoga and Bhakti Yoga) and revealed his universal form. Even today the 700 verses of the Gita show all of humanity the way to live.