Raajaa Shalya also heard that Paandav's exile period was over, so he wanted to see them. Bu as he was thinking this, a messenger came from Yudhishthir that he should be ready for war. So he left his city for Upaplavya with his one Akshauhinee army. Duryodhan heard that Shalya had left his city to Upaplavya, so he decided to please him. He made all kinds of arrangements for comfort and entertainment for him at many places on his way. Many edibles, many tanks of drinks, roomy apartments were provided by him. And arriving at those spots they were treated like Devtaa. Shalya did not fix his own camp for seven days. Shalya was very pleased with the arrangements, he thought that it was done by Paandav. Once he asked the servants as where were his hosts, so that he could thank them and reward them, but the servants didn't know what to say, so they went to Duryodhan and told them everything.

Duryodhan went to the camp of Shalya and met him. Shalya was stunned to see him there and to know that Duryodhan was doing all this to him. He was very pleased with him, he said - "I said I will reward him who has taken such a good care of me. What can I do for you?" Duryodhan fell on his feet and said - "Please be with me in this war as my Commander-in-Chief." Shalya said - "Be it so. And what else I can do for you?" Duryodhan danced with happiness saying, "It is done, it is done." Shalya said - "You may go back to your city. Let me pay a visit to Paandav first." Duryodhan said - "After seeing the Paandav you come back soon, I depend on you." Shalya said - "You may go back to your city without any doubts. I will surely come back soon." Then they embraced each other and departed to their respective places.

According to Mahaabhaarat Serial (seems logical)
On asking by Duryodhan Shalya said - "I cannot accept this position while Bheeshm is there." At this Karn said - "Then you accept to become my Saarathee." Shalya accepted this. Beacuse after Krishn there was no better Saarathee than Shalya at that time. This had changed the line of fight between Karn and Arjun.

Poor Shalya did not know what to do with Duryodhan, but since he had already made the promise, he had to keep it. He said - "I came on the invitation of my nephews, but you have won my heart, so I will surely please you. I will fight with my nephews, but first I must go to Yudhishthir and talk to him. I want to give him my blessings." Duryodhan couldn't have said "No" to this, so he let him go but asked him to come back soon.

Shalya went to see Paandav. They welcomed him and greeted him dearly. He accepted their welcome. He asked their welfare and said - "I am very happy to see you alive and well after these 13 years. It was indeed difficult task to complete the term. You will certainly get happiness after killing your enemies." Then they sat and talked for some time. Shalya told about the recent development - his meeting with Duryodhan, his promise to him. Yudhishthir was greatly disappointed but since he knew Dharm he didn't mind it. He just said - "It will be very unfortunate that we will have to fight with our own Maamaa in this war." Shalya himself was very sad at this but was helpless. He said - "I wish it did not happen like this." Krishn said - "At lease you will give your blessings to Paandav?" Hearing this Nakul and Sahadev got very sad, but what could they do then. Sahadev was most sad. In that mood he misbehaved with Shalya. Arjun said to him - "If Maamaa is fighting from Duryodhan's side, it doesn't mean that he loves Duryodhan more than you. Go and ask for pardon for your behavior." Sahadev went to him and asked for his pardon.

Then Yudhishthir said - "Please do us a favor, I am not worried about anybody in this war but Karn. When the fight between Karn and Arjun takes place, you may be asked to be his charioteer. You are like Krishn in the art of driving chariot, so when that fateful day comes you must protect Arjun. Although this is an improper thing to ask you to do, but you must do it." Shalya assured him to do so at his best. He said - "If there is anything else he will have to do for their good, he will surely do it without their request. Your bad days are over, you will rule the earth, this is my blessing to you. Destiny is all powerful, think in this line and do your duties righteously. Even Devtaa have to suffer miseries, like Indra suffered with his wife." Yudhishthir asked about Indra as how he suffered with his wife. Then Shalya told him the story of Indra and Twashtaa. (Story of Indra and Twashtaa).

Then he went away with a heavy heart because whatever he was doing, it was not in his plan.

Paandav's and Kaurav's Armies

The friends of both sides started coming in. Some went to Upaplavya. The first one to come was Saatyaki with his one Akshauhinee army. The next was Chedi king Dhrishtketu to arrive there with his one Akshauhinee army. Next was Jayatsen, the king of Magadh, the son of Jaraasandh, with his one Akshauhinee army. The next came the five Kekaya brothers with their one Akshauhinee army. Then came Drupad, also with one Akshauhinee army. He brought his own sons Dhrishtdyumn and Shikhandee and Draupadee's five sons too along with him. Viraat came with one Akshauhinee army along with his sons and brothers. The king Paandya also came with his one Akshauhinee army. So altogether Paandav had seven Akshauhinee army.

Hastinaapur was not also behind. Friends of Duryodhan were trickling in with their armies. First came Bhagadatt with his one Akshauhinee army. Then came Raajaa Shalya with his one Akshauhinee army. Bhoorishravaa, Kritvarmaa, Jayadrath, Sudakshinaa (the king of Kaamboj), Vind and Anuvind (two kings of Avantee known as Avantee brothers) also came with one Akshauhinee army each. Jayadrath also came with his one Akshauhinee army. The king Neel of Mahishmatee Nagaree also came. There were many others whose army made up about three Akshauhinee army. So altogether Duryodhan had 11 Akshauhinee army in comparison to Paandav's seven Akshauhinee army. There was no space in the city of Hastinaapur to stay even for chief warriors of Duryodhan's army. And for that reason, the land of five rivers, whole of Kurujaangal, the wild forest of Rohitak, the Ahichatra, and Kaalkoot, the banks of Gangaa and Varanaa, the hill tracts of the border of Yamunaa, were entirely overspread with Kaurav army. And the messenger, the Paanchaal sent, saw this army.