Parasurama's vow to kill all Kshatriyas

Once when Parasurama was away from his home one King Karthiveerarjuna came to the abode of Jamathgni, the father of Parasurama  and was felicitated by the sage with food and drinks provided by the holy cow Kamadhanu because of its divine powers.

King Karthiveerarjuna was a very powerful king with 20 hands and had divine powers.  The king was so much impressed by the cow and wanted the cow for himself and asked the sage to hand over the cow to him.

 The sage refused saying the cow came to him from heaven and cannot be gifted away without its permission and he wanted the cow to have milk and other items for his daily routines and also for entertaining Kings and others like him.

The King was offended as his request was turned down and then the king with his army  tried to forcefully take the cow away from Jamathagni but the holy cow sent  a large force of army  with its holy power to fight the king's army. There was a fierce battle  but they were defeated by the King’s army and they also killed the Sage and his sons and took away the cow Kamadhanu.

When Parasurama came back, he saw to his horror what has happened and with grief and rage went to fight the king Karthiveerarjuna and defeated him and his army and destroyed all of them. Then with the same fury he went to kill all Shatriya kings and Shatriyas as Kings come from the caste of Kshatriya. He went on doing it until he met Rama, the son of Dasaratha, the  King of Ayodhya. Rama was also a reincarnation of Lord Vishnu and was equal to Parasurama in valour and strength  and hence when Parasurama challenged Rama, Rama was able to hold him and Parasurama accepted his defeat and gave his powers to Rama and left to do penance.