The Battle of the Ten Kings () is a battle, first alluded to in the 7th Mandala of the Rigveda (RV), between a king of the Bharatas and a confederation of tribes. It resulted in a decisive victory for the Bharatas and subsequent formation of the Kuru polity. It is possible that the Battle of the Ten Kings, mentioned in the Rigveda, may have "formed the 'nucleus' of story" of the Kurukshetra War, though it was greatly expanded and modified in the Mahabharata's account.
In Book 3, the Bharatas are noted to have crossed Beas and Sutlej, in their progress towards Kurukshetra where they came across a nascent (and temporary) inter-tribal alliance. This led to the battle, which is described in the 18th hymn (verses 5-21) of Book 7; the exact motivations are doubtful — Michael Witzel argues that it might have been a product of intratribal resentment or intrigues of an ousted family-priest while Ranabir Chakravarti argues that the battle was probably fought for controlling the rivers, which were a lifeline for irrigation. The hymns also makes mention of the tribes seeking to steal cows from the Bharatas.
Battle
Hanns-Peter Schmidt, whom Witzel deems to have produced the most "detailed, and ingenious reinterpretation" of the hymns, locates a unique poetic moment across the RV corpus, in their extraordinarily abundant usage of sarcastic allusions, similes and puns to mock the tribal alliance. Some of those allusions seem to be heavily context-specific and (still) remain unrecognized; there exist considerable disputes about interpretations of particular words, in light of the employed figures of speech and other poetic devices.
First phase
The first phase of the battle took place on the banks of the river Ravi (then Parusni) near Manusa, west of Kurukshetra. The Bharata King and their priest are respectively mentioned as Sudas Paijavana and Vasistha, in the Rig Veda; however the names change in Samaveda and Yajurveda Samhitas. The principal antagonist is doubtful and names of the participating tribes are difficult to retrieve, in light of the phonological deformations of their names. Plausible belligerents of the tribal union include (in order) — Purus (erstwhile master-tribe of Bharatas), Yadu (probably commanded by Turvasa), Yaksu (relatively unimportant or a pun for Yadu), Matsyas, Druhyus, Pakthas, Bhalanas, Alinas, Vishanins, Sivas, Vaikarna, and Anu.
Though seemingly an unequal battle, going by the numbers (this aspect is highlighted multiple times in the hymns), Sudas decisively won against the tribal alliance by strategic breaching of a dyke on the river thereby drowning most (?) of the opponents. This sudden change in fortunes is attributed to the benevolence and strategizing of Indra, the patron-God of Bharatas, whose blessings were secured by Vasistha's poetics.
Second phase
Thereafter, the battleground (probably) shifted to the banks of river Yamuna, wherein the local chieftain Bhida was defeated along with three other tribes — Ajas, Śighras, and the Yakṣus.
Aftermath
The Battle of the Ten Kings led Bharatas to occupy the entire Puru territory (Western Punjab) centered around Sarasvati River and complete their east-ward migration. Sudas celebrated his victory with the Ashvamedha ritual to commemorate the establishment of a realm, free of enemies from the north, east, and west. He still had enemies in the Khāṇḍava Forest to the south, which was inhabited by the despised non-Indo-Aryan Kikatas.
A political realignment between Purus and Bharatas probably followed soon enough and might have included other factions of the tribal union as well; this is exhibited from how the core collection of RV prominently features clan-hymns of both the sides.
Historicity
Numerous translators since the 1800s including K. F. Geldner have considered the battle as a historical event, based on the narration-characteristics of the verses. Witzel dates the battle between approximately 1450 and 1300 BCE; he deems the concerned hymns to be late interpolations. Stephanie W. Jamison warns against using it as a major source to reconstruct history since the description of the battle is "anything but clear."
Both Witzel and Jamison find the very next hymn (7.19, verse 3) to show a striking shift of allegiance with Indra helping Sudas as well the Purus, who won land.