After the fall of Bhisma, Doryodhana wanted Karna to be the
next commander-in-chief. He knew that Karna was capable of defeating
Arjuna and asked him to take charge of the army. However Karna asked
Duryodhana to make Drona the commander-in-chief as this would be
acceptable to everyone. Duryodhana liked the idea and Dronacharya was made
the commander-in-chief. The Kaurava army got a new breath of life because
they were sure that the brave guru would lead them to victory. Karna had
pledged that he would not fight under Drona, so he left the battlefield.
But Drona requested him to forget all grudges and joined the battle for
the sake of his friend, Duryodhana. To everybody's joy, Karna agreed and
joined the battle. Duryodhana knew that Drona would never kill any of
the Pandavas so he asked him to capture Yudhisthira alive. Drona did not
mind carrying out this order and rearranged the army to achieve this end.