What is the story of Parshuram

Why did Bhishma fight with Lord Parashurama?

Bhishma tells the story in the Udyoga Parva of the Mahabharata, but first some background information. Bhishma was the son of Shantanu, king of Hastinapura, and the goddess Ganga. But Ganga left Shantanu, and Shantanu later fell in love with a woman named Satyavati. But Satyavati's (adopted) father Matsyagandha, the chief of a fishing tribe, would not consent to the marriage because he feared that Bhishma and his descendants would rule Hastinapura and not Satyavati's children. So Bhishma made a vow that he would never become king and that he would remain celibate so that his descendants would never claim the throne. (Because of this terrible vow he was given the name "Bhishma" or "Terrible".) Then Matsyagandha consented to the marriage, and in the course of time Shantanu and Satyavati had two sons, Vichitravirya and Chitrangadaa. When Shantanu died, Chitrangada became king, but he died soon after a confrontation with a Gandharva because the two had the same name (yes, really!).

So the throne now fell to Vichitravirya, who had no wives, but Bhishma heard that the king of Kashi held a Swayamvara for his daughters Amba, Ambika and Ambilika. So Bhishma went to Kashi to win these princesses over to Vichitravirya. He kidnapped the three princesses, fought all the kings of the world when they tried to stop him, and brought them back to Hastinapura. But then the eldest princess informed Amba Bhishma that she was in love with a king named Shalva, so Bhishma allowed her to return to him. But Shalva wasn't ready to take her back because she'd been kidnapped by another man.

Amba was furious that Bhisma was ruining her life. To seek revenge, she went to Parashurama and asked for his help in killing Bhishma. Parashurama was reluctant to do so, both because Bhishma was his former disciple and because he had made a vow that he would no longer take up arms. But the sage Akritavana told Parashurama that it was not right to leave someone whom you promised to help, and then reminded him that under certain circumstances he had made an additional vow to take up arms:

This was also, oh great Muni, the vow you made back then, oh Rama ... that you would kill the person in battle, be it a Brahmana, a Kshatriya, a Vaisya or a Sudra who would be an enemy the Brahmins. You had further promised that as long as you lived you would not abandon those who would come to you in horror and seek your protection, and that you would ... kill this proud warrior who would defeat all assembled Kshatriyas of the earth in battle !

And since Bhishma had defeated all the kings of the world in battle when the three princesses were kidnapped, Parashurama was allowed to fight him. And so he said: "If I take this girl with me, I will take myself to the place where Bhishma is. If Bhishma, proud of his successes in battle, disobeys my command, I will kill this arrogant Wight. That is also my fixed solution. "

So Parashurama went to Kurukshetra, the future site of the Mahabharata War, and asked Bhishma to come there. Bhishma came immediately and was dying to see his former guru. Then Parashurama asked Bhishma to marry Amba as no one else would marry her after he was kidnapped. But Bhishma said he could not marry her himself because of his vow of celibacy, and he could not give her to his brother Vichitravirya because he had already promised to let her go to Shalva:

Oh Brahmana, there is no way I can give this girl to my brother. O you of the Bhrigus race, for me she said: I am Salwa! And from me she was allowed to go to Salwa's city. Regarding myself, even this is my firm vow that I cannot give up Kshatriya practices out of fear or compassion or avarice for wealth or lust!

So Parashurama had no choice but to try to kill him. So Guru and Shishya had to fight. Now Bhishma was wearing armor and was sitting in a chariot while Parashurama was only on foot, so Bhishma offered him weapons and a chariot, but Parashurama said that he did not need such things as he was an incarnation of Vishnu:

The earth, oh Bhishma, is my car, and Vedas are like good horses, the animals that carry me! The wind is my motorist, and my armor is made up of these mothers in the Vedas (Gayatri, Savitri and Saraswati). Well covered by these in battle, oh son of Kuru's race, I shall fight!

And so began the first great battle in Kurukshetra. The better known Kurukshetra War between the Pandavas and Kauravas lasted 18 days, but the war between these two heroes lasted 24 days. On the 23rd night, Bhishma had tried all the maneuvers and weapons he could think of, but none of them could defeat Parashurama, so he prayed that the gods would suggest a way to victory while he slept. (Like the Mahabharata War, this Kurukshetra battle was fought every day between sunrise and sunset.) Indeed, the gods told him in a dream that they would give him the knowledge of Prashwapastra, a weapon formerly used by the god Dyaus Pita was used (because Bhishma is an incarnation of Dyau's Pita):

Get up, oh Ganga's son, don't be afraid! We will protect you because you are our own body! Rama, the son of Jamadagni, will never be able to defeat you in battle! You, O bull of Bharata's race, will be the conqueror of Rama in battle! This beloved weapon, O Bharata, called Praswapa, which belongs to the Lord of all creatures and was forged by the divine artisan, will come to your knowledge, for it was known to you in your previous life! Neither Rama nor anyone on earth knows it. So remember it, poor mighty arm, and apply it forcefully! O king of kings, o sinless one, it will come to you! ...! The son of Jamadagni, affected by the power of this weapon of yours, will fall asleep!

The next day, Bhishma suddenly acquired the knowledge of pashwapastra, but when he tried to use it, Narada and other gods came and stopped him. Here is Bhishma's account of it:

When I aimed at it, Narada approached me and said, "Over there, O Kauravya, the gods stay in the sky! They forbid you too today! Do not point the praswapa weapon! Rama is an ascetic who has Brahma merits and he is your teacher again! Never, Kauravya, humiliate him. "As Narada was telling me this, I saw these eight utterances of Brahma stationed in the sky. Smiling, O King, they slowly said to me, "O chief of the Bharatas, even do what Narada says. Even that, O best of Bharatas, is of great use to the world!"

And shortly afterwards Parashurama was approached by the spirits of his ancestors who also told him to stop fighting because Parashurama should no longer behave like a Kshatriya and because Bhishma was destined to die at the hands of someone else:

Oh father, never show such rash again, the rash, namely to fight with Bhishma or especially with a Kshatriya, oh descendant of the Bhrigu race, is the duty of a Kshatriya! The study (of the Vedas) and the practice of the vows are the greatest wealth of the Brahmins! For some reason you had previously been instructed by us to take up arms ... Let this fight with Bhishma be your very last, because you've had enough of it already ... Bhishma is one of the leaders of Vasus! ... -How can he be defeated by you? So stop, oh Bhargava! This foremost of the Pandavas, Arjuna, the mighty son of Indra, was created by self-creation to be the slayer of Bhishma!

And so, after some controversy, Parashurama agreed to lay down his arms and surrender. He told Amba that he could not defeat Bhishma and that Bhishma was the one to whom she should seek refuge. But Amba was not interested in anything but revenge at the time, and she said this:

I myself will not go to Bhishma a second time. However, O perpetrator of the Bhrigus race, I will go there, O you rich in asceticism, where I can kill Bhishma in battle!

So she engaged in tapasya (deep meditation) until Shiva appeared before her and she asked to be reborn as a man so that she could kill Bhishma. Shiva granted her the blessing and Amba immediately jumped into the fire. She was reborn as Draupadi's brother Shikhandi, who was instrumental in Bhishma's death because Bhishma was unwilling to fight someone who had been a woman in a previous life.

sv.

To answer OP's second question: And who won the fight? did it end in a peace treaty or Bhishma won it? You might want to add that in bold at the very beginning or at the end.