Arjun was the best archer and had a very thorough knowledge of other warfare games. Arjun was the only one who knew to fight in Chakra Vyooh. He knew to enter it as well as to come out from it. And he was the bravest warrior in Paandav's army. Till he was in the battlefield nobody could defeat Paandav. Kaurav also knew this. So there seemed no end of war. So Dronaachaarya thought that if Arjun can be killed then also the war will end. And since only Arjun knew the tactics of Chakra Vyooh, nobody else will be there to fight. Drone handed over its organization to Jayadrath.

In this Vyooh, there are four circles, one inside the other. It worked like this that the outermost circles soldiers stood facing front, and as the opponent entered the first circle its warriors turned around showing their back so that nobody else could come inside.

In the innermost circle warriors were standing facing outside, that was why no one could come out of the innermost circle unless he backstabs any one warrior to make space for himself, which is illegal. Inside the innermost circle there was another circle of 6 warriors and in between them was standing Karn. 

Now the situation was that Kaurav wanted to kill Arjun. Krishn wouldn't lift any weapon according to His vow. Arjun cannot kill Karn because he had Kavach and Kundal. So it was very easy, as only Karn could kill Arjun, Arjun should be allowed to enter the Chakra Vyooh, and then Karn should kill him. After that war was easy. But Krishn was not in favor of happening this. 

So next day Drone's plan was implemented. In the battlefield the Chakra Vyooh was created by Dronaachaarya Jee. Inside the innermost circle were 7 people to fight with Arjun: Duryodhan, Dronaachaarya, Kripaachaarya, Karn, Ashwatthaamaa, Shakuni and Jayadrath.

Now Krishn knew that Drone had planned for Chakra Vyooh and if Arjun had gone there, he could not be saved, so He cleverly instigated Arjun to fight with two kings. The two kings got scared of Arjun and ran away from the battlefield. Arjun followed them and they took him very far. So far that he could not return till evening.

In the battlefield all were waiting for Arjun to come there, but later they found only a child coming towards them. In fact nobody else knew to break that Vyooh except Arjun. Paandav tried to look for Arjun but they couldn't see him anywhere. Abhimanyu said - "I know how to enter it, but I don't know how to come out from it." His all uncles said - "We will be there as your backup. As you will break the first gate (there are four gates of the Vyooh) we will also enter behind you. Thus we will always be behind you." Besides Paandav were sure that there will be no injustice in the war.

Abhimanyu got ready. Paandav also followed Abhimanyu. But unfortunately as he entered the first gate, Paandav were stopped then and there only. They could not enter even the first gate. Abhimanyu freely entered the Vyooh. There he fought alone very bravely with seven great warriors - Duryodhan, Dronaachaarya, Kripaachaarya, Karn, Ashwatthaamaa, Shakuni and Jayadrath. Karn did not fight with that child, he was waiting only for Arjun. When he did not see Arjun he got disappointed and stood at one side. 

Since Abhimanyu didn't know coming out from it, he could not come out of it. Soon he lost his weapons, chariot, Saarathee etc. He had no weapon to defend himself. Seriously wounded he fell down on the ground. Kripaachaarya Jee advised Kaurav not to attack him as he had nothing to fight, but Jayadrath didn't listen to him. He kicked him with his foot and killed him with his sword. He was only 16 years old at that time.

When evening was about to fall, Arjun remembered, that he was away from the battlefield for the whole day, what would have happened there back in the battlefield without him? So he immediately rushed back. But by then his brave son had been killed by Kaurav army by cheating in an unjustified way.

In the evening when Arjun came back after following the two kings, he came to know about his son's death. He also came to know that Jayadrath killed his teenage son in an unjustified way, so he vowed to kill Jayadrath before the sunset next day; or if he could not kill him before the sunset then to immolate himself. 

When Jayadrath knew about this he got frightened. He asked refuge to Duryodhan. Duryodhan assured him for his safety. The whole day Kaurav army surrounded him. Many soldiers lost their lives, but it was almost impossible to attack Jayadrath. Morning turned to noon, and noon into afternoon. Paandav were getting worried, and Kaurav appeared to rejoice.

As the evening fell, Jayadrath got very happy that now he was saved and Arjun would have to die. He thought he was out of danger so he started dancing with joy. Skies had got dark, and it seemed to all people that the Sun had set and Arjun had to die according to his vow. So Arjun started preparing a pyre for himself, as he could not fulfill his vow. On the other side Jayadrath was happy saying, "The Sun has set, your vow is not fulfilled, you will have to die now."

Arjun was sorry for this and as he was about to enter the Agni, the Sun came out. Krishn immediately said to Arjun, "Arjun, Wait, the Sun has come out. Now you can fulfill your vow. What are you waiting for? Kill Jayadrath, it is still daytime." Immediately Arjun picked his bow and shot an arrow at Jayadrath. It cut his head and threw it in his father's lap. Krishn had already warned him that he should cut Jayadrath's head in such a way that it should not fall down on the ground, but should fall in his father's lap.

My Note
1. There are two versions of this incident (of sunset). According to one version on that day, at that hour, there was a solar eclipse, so because of the solar eclipse it seemed to all that the evening fell, while the Sun was not seen only because of that eclipse. When it came out of the eclipse, it was seen and thus it was still day time.