Before the start of Mahabharata war, both Arjun and Duryodhan visited Krishna asking for help. Duryodhan had reached Krishna before Arjun and sat near his head. Arjun came after Duryodhan and sat near krishna’s feet. When Krishna woke up and opened his eyes, Arjun was the first one he saw and as a result asked him about his purpose of visit.

However, since Duryodhan arrived before Arjun, he got angry and complained that he came first. To this, Krishna replied that since he saw Arjun first therefore, his wish would be fulfilled first. Arjun given the chance asks Krishna to come to his side, leaving Duryodhan more than happy, as he wanted the army and not unarmed Krishna.

Prior to the war, both Arjun and Duryodhan had a choice between Krishna and his armed forces. Arjun had joyfully picked Krishna and Duryodhan cheerfully picked the armed force, so it was not Krishna who really gave his army to the Kauravas.

In fact, Krishna played it smartly because he knew that Arjun would prefer him and Duryodhan, who never thought of Krishna as God, would go for the powerful army instead. He never wanted to be at the Kaurava’s side since the start. This deal also made both Arjun and Duryodhan satisfied.

But during all this, Krishna had another motive. His aim was to get the subcontinent rid of the powerful warriors, and restore the balance. Because at that time Kings possessed too much power and that power challenged the peace of the overall society. During this mission, he wanted his powerful army too to be perished. Thus, he granted Duryodana’s wish and handed them to the Kauravas.

Incidentally, it was Arjun who destroyed a large extent Krishna’s army, with Krishna’s support as his charioteer. Krishna’s army battled with Samsaptakas against Arjun, and as a result, he was the one who exterminated all of them.

According to Kshatriya rules, Krishna did not have to help Duryodana. Warriors always had the right to help their friends no matter what the other side asked. Only a person who has any no affiliation to either side can choose to help the side that approaches him first. We can also see that most of the important allies of Kauravas and Pandavas chosen their sides based on their friendships and previous enmities.

Personally, Krishna was always with Pandavas but, officially his Kingdom had an equal political relationship with both Pandavas and Kauravas. Thus he decided to provide some help to Duryodhan too in order to accomplish his other plans.