Kuru Kingdom
Panchalas were the closest among all the allies of the Pandavas in the Kurukshetra War. Panchala prince Dhristadyumna was the commander-in-chief for the whole of the Pandava army. Many heroes from Panchala battled in the war. Most of them were alive till the end of the war. However all of them were slain by Ashwathama in an ambush, when they were asleep in their tents, on the last day of the war. Ashwathama was the ruler of half of the Panchala Kingdom viz the northern Panchala, under Kuru king Duryodhana. Northern Panchala was then reduced to the status of a province of the Kuru Kingdom. This could be the political factor that caused the Panchalas (southern Panchalas) to become kinsmen of the Pandavas, who were a rebel force in the Kuru Kingdom. By supporting the Pandavas in Kurukshetra War they might have sought to regain their lost Panchala territories.