Lord Krishna stood along with the Pandavas during the battle at Kurukshetra.
What is the exact reason for this?
I am answering this question with the assumption that O.P wanted to know what the story was which resulted in
Krishna siding with the
Pandavas and not the
Kauravas during the war.
This was part of the rendition of the epic as a
TV series on DD1. The scene is played out in the following manner.
Just before the start of war both Arjuna and Duryodhana decide to visit Krishna to convince him to join their respective sides. Duryodhana reaches Krishna's palace first and finds Krishna sleeping. He decides to wait for him to wake up and sits on a stool beside Krishna's head. Arjuna enters a few minutes later, finds Krishna sleeping and also decides to wait. He finds a seat near Krishna's feet.
Krishna wakes up after a while and his eyes fall on Arjuna first as he had been sitting in the direction of his eye sight. And Krishna immediately upon waking up asks Arjuna about the reason for his visit. Arjuna requests that Krishna and his massive Yadava army join hands with the Pandavas during the war.
Duryodhana, who by then understands that Krishna might say yes before asking him why he had come, interrupts the conversation and tells Krishna that even he had the same request. And since he had come there first Krishna must entertain his request first. Krishna, who in his heart has already decided to side with the Pandavas, comes up with an ingenious way of reaching a settlement. Krishna says he will divide the requested item into 2 parts and will let them choose which part each one wants to have during the war. This, he tells Duryodhana, is because he is trying to accommodate the request of both his cousins. One part is Krishna alone (who will wield no arms and not strike a single blow on the battlefield). The other part is the entire Yadava army with weapons of all kinds.
He also tells Duryodhana that it has been unfortunate that upon waking up his eyes first fell on Arjuna, and as he had already asked Arjuna for the reason for his presence, and hence he was honour bound to give Arjuna first choice. Duryodhana reluctantly agrees to this.
Arjuna chooses Krishna and tells him that he willings agrees to his condition of not taking up arms during the battle. Duryodhana, at this point, is unable to believe his luck. He feels that Arjuna has made the biggest mistake of his life. He thanks Krishna for his offer and gleefully leaves the room. Krishna is seen with a gentle and enigmatic smile playing on his lips.
hope it helps :)
This incident is mentioned in Udyoga Parva of Mahabharata. The story goes like this: When it was confirmed that the war is certain, then both Duryodhana and Arjuna went to seek help of Lord Krishna. Duryodhana arrived first and sat near the head of Lord Krishna and Arjuna arrived second and stood at the back of bed. When Lord Krishna awake he saw Arjuna first so he asked the reason for coming to Arjuna but as Duryodhana had arrived first, so he (Duryodhana) wanted to be noticed first. But as Lord Krishna had seen Arjuna first and also Arjuna was junior to Duryodhana in age. So, Arjuna got the priority to choose between Lord Krishna (without weapons) and His Narayana army. Arjuna had selected Lord and at last Duryodhana was happy after getting Narayana army.
And as Krishna was sleeping, Duryodhana entered the room, and sat down on a fine seat at the head of the bed. And after him entered that wearer of the diadem the magnanimous Arjuna. And stood at the back of the bed, bowing and joining his hands. And when the descendant of Vrishni, Krishna awoke, he first cast his eyes on Arjuna. And having asked them as to the safety of their journey, and having fitly bestowed his greetings upon them, the slayer of Madhu questioned them as to the occasion of their visit.
Then Duryodhana addressed Krishna, with a cheerful countenance, saying, It behoveth you to lend me your help in the impending war. Arjuna and myself are both equally your friends. And, O descendant of Madhu, you also bear the same relationship to both of us. And today, O slayer of Madhu, I have been the first to come to you. Right-minded persons take up the cause of him who comes first to them. This is how the ancients acted. And, O Krishna, you stand at the very top of all right-minded persons in the world, and are always respected. I ask you to follow the rule of conduct observed by rightminded men.
' Thereat Krishna replied, 'That you have come first, O king, I do not in the least doubt. But, O king, the son of Kunti, Dhananjaya, has been first beheld by me. On account of your first arrival, and on account of my having beheld Arjuna first, I shall, no doubt, lend my assistance, O Suyodhana, to both. But it is said that those who are junior in years should have the first choice. Therefore, Dhananjaya, the son of Kunti, is entitled to first choice. There is a large body of cowherds numbering ten crores, rivalling me in strength and known as the Narayanas, all of whom are able to fight in the thick of battle. These soldiers, irresistible in battle, shall be sent to one of you and I alone, resolved not to fight on the field, and laying down my arms, will go to the other. You may, O son of Kunti, first select whichever of these two commends itself to you. For, according to law, you have the right to the first choice.'
'Thus addressed by Krishna, Dhananjaya the son of Kunti selected Kesava who was not to fight on the battle-field, even Narayana himself, the slayer of foes, increate, born among men at his own will,--the foremost of all Kshatriyas and above all the gods and the Danavas. And Duryodhana selected for himself that entire army (composed of the Narayanas). And, O descendant of Bharata, having obtained those troops numbering thousands upon thousands, he was exceedingly delighted, although he knew that Krishna was not on his side.
Here is another story : Arjuna and Krishna are often referred to as Nara-Narayana in the Mahabharata and are considered part incarnations of Nara and Narayana respectively, according to the Bhagavata Purana
In a previous life, the duo were born as the sages Nara and Narayana, and who performed great penances at the holy spot of Badrinath. Nara and Narayana were the Fifth Avatar of Lord Vishnu. The twins were sons of Dharma, the son of Brahma and his wife Murti (Daughter Of Daksha) or Ahimsa. They live at Badrika performing severe austerities and meditation for the welfare of the world. These two inseparable sages took avatars on earth for the welfare of mankind .Legend has it that once Lord Shiva tried to bring the fame of Nara and Narayana before the entire world. To do that, he hurled his own potent weapon Paashupathastra at the meditating rishis. The power of their meditation was so intense that the astra lost its power before them. Lord Shiva stated that this happened since the duo were jnanis of the first order constantly in the state of Nirvikalpa Samadhi.
As it says they were inseparable, therefore Krishna stood with pandavas.
The story we all read & know. Krishna was in the side of pandava everybody knows. When question is coming as why then we have to analysis the story properly. Krishna is the God & hence supreme in all respect. Indirectly speaking there is no other authority who can make Krishna answerable to it. But it is the God's own choice to follow some good practice & support them. He is very often called as bhakti batsal. It is true. But who are the bhakta of the God. It is not simple to be his Bhakta. There are certain rule , regulation & discipline to follow. Once you are following all the guide line then everybody( all the good natured person) will love you. Normally Krishna like the talents with a good code of conduct which was with pandava. That is why god was in their side.