The Pandavas spent thirteen years in exile according to the conditions of the dice game.
However, the inevitable happened and Duryodhana refused to give Indraprastha back to the Pandavas. War was the verdict.
Being the Royal teacher of Hastinapur, Dronacharya and Kripacharya fought on the side of the Kauravas. Ashwattaman, was already drawn towards the Kauravas and also fought on their side.
Bhishma was the eldest and was a formidable warrior. So for the first ten days of the battle, Bhishma was made as the general of the army.
Using Shikhandi, Drauapdi’s sibling, the Pandavas incapacitated Bhishma. For the remaining 8 days of the battle, Bhishma was lying on the bed of arrows as he watched the battle unfold .
(Shikhandi was Amba reborn. Amba was the Princess of Kashi, and wanted to marry Bhishma. When Bhishma refused to marry her, Amba vowed to be the cause of Bhishma’s death and killed herself. Amba was reborn as Shikhandin, the daughter of the Princess of Panchala. Even as Shikhandin, she remembered who she was in her past life and prayed to a yaksha in the forest. The yaksha converted Shikhandin into a man.
Bhishma had taken a vow that he would never fire a weapon against a woman or children. As Shikhandi was originally a female, Bhishma refused to engage in battle with Shikhandi. Shikhandi went with Arjuna in his chariot on the tenth day. Bhishma refused to fire at Shikhandi allowing Arjuna to incapacitate Bhishma. However the interesting part is that in this story, the Pandavas looking at how much damage Bhishma was causing to the Pandava army, went to Bhishma and asked him the advice on how they could defeat him. Bhishma himself gave the Pandavas the way of killing him!)
After Bhishma fell, the first thing which happened was that Karna was called to fight the battle. When Bhishma assumed the command of the Kaurava army, the first condition that Bhishma imposed was that he did not want Karna to be fighting in his army. (The reason given by Bhishma for not letting Karna fight was that Karna was taught by Parashurama, whom Bhishma thought of as an enemy. Both Bhishma and Karna were taught by Parashurama. However when Bhishma spurned Amba’s proposal to marry her, Amba went to many kings to have Bhishma killed. None of the kings were brave enough to fight Bhishma. The only person who came forward to fight for Amba was Parashurama. Both Parashurama and Bhishma fought for a long time. However Parashurama withdrew from the fight saying that he could not win this fight. It was only after this that Amba killed herself. As Parashurama had fought with Bhishma, Bhishma was angry with him and hence refused to let Karna, Parashurama’s disciple, fight. However there could be another reason also. Bhishma was one of the few people in the Kaurava army who knew of Karna’s origin. Bhishma knew that Karna was the son of Kunti and he wanted to make sure that all the six sons of Kunti survived the war, which could be why Bhishma refused to let Karna fight)
Almost everyone in the Kaurava army wanted Karna to succeed Bhishma, but then Karna was a smart warrior. He realized that he was neither the eldest in the Kaurava army nor did he have the respect of the entire Kaurava army (Karna was always considered as a charioteer’s son and throughout the epic, he was never respected as a warrior.) Karna realized that for any army to win the war it was important not to have any internal strife between the warriors. So Karna performed a brilliant move to avert any misgivings. He suggested the name of Drona as the commander of the Kaurava army.
Duryodhana gladly accepted the suggestion and so Dronacharya was made the general of the army.
Drona was shocked. The newfound position made the simple Dronacharya think that Duryodhana actually trusted him. In a spur of the moment, Dronacharya looked at Duryodhana proudly and told him. ‘Ask me any boon in the battle and I will grant it to you!’
Duryodhana smiled. ‘Bring Yudhishtara to me, alive!’ was all he said.
‘Alive?’ Drona asked surprised.
Duryodhana nodded. ‘If you kill Yudhishtara, you will bring in the wrath of Arjuna!’ Duryodhana almost shuddered as he continued. ‘And he would possibly destroy all of us, the very same day! So….please bring Yudhishtara alive! I can make Yudhishtara play dice with me! And I will make sure Yudhishtara is exiled again….Yudhishtara is a man of his words! If he lost, he would walk away and the Pandavas would follow him! There would be no further bloodshed!’ Duryodhana said triumphantly.
Dronacharya looked at the Pandava army at a distance and turned to Duryodhana. ‘If Arjuna is not there with Yudhishtara….!’ Drona smiled faintly. ‘Yudhishtara would be here, tied and bound, by sundown!’