Why Bhishma vs Parsuram Duel

Bhishma was a great archer and a warrior. In the process of finding a bride for his half-brother the young king Vichitravirya, Bhishma cleverly abducted princesses Amba, Ambika and Ambalika of Kashi (Varanasi) from the assemblage of suitors at their swayamvara. Salwa, the ruler of Saubala, and Amba (the eldest princess) were in love. Upon reaching Hastinapura, Amba confided in Bhishma that she wished to wed Salwa. Bhishma then sent her back to Salwa who turned her down as it was humiliating for a man to accept a woman who had been so long in the company of another man. She then naturally approached Bhishma for marriage who refused her, citing his oath. Amba, humiliated and enraged beyond measure, vowed to avenge herself against Bhishma even if it meant being reborn over and over again. Legend has it that at her maternal grandfather’s suggestion Amba sought refuge with Parasurama who ordered Bhishma to marry Amba. Bhishma politely refused saying that he was ready to give up his life at the command of his teacher but not the promise that he had made. Upon the refusal, Parasurama called him for a fight at Kurukshetra.