Dronacharya, the son of Rishi Bharadwaja, was trained in the ashram of Sage Bharadwaja along with Drupada, the prince of Panchala. Both youngsters became best friends, and Drupada promised Drona that he would give him half of his kingdom.
Years later, Drupada became the king and forgot his promise, while Dronacharya excelled in warfare and married Kripi, the sister of Kripacharya, who had trained Pandu and Dhritarashtra.
Ashwatthama, the son of Dronacharya, had a divine gem on his forehead. Once, he saw his friends drinking milk and wished to drink some too. His friends, playfully, gave him water mixed with flour. Dronacharya felt ashamed, as he could not even afford milk for his son.
Hoping Drupada would help him, Dronacharya went to meet him and asked for his share of the kingdom, as once promised. But Drupada had forgotten about his promise and insulted Dronacharya, saying that someone like him should ask for alms, not a share of the kingdom, and that a king could not befriend someone like him. Angered by the humiliation, Dronacharya wanted Revenge against Drupada.