The history of India can conveniently divided into following epochs.
Vedic epoch comprises of all the migrations, invasions, sociology of the period of time which is immortalized in the verses of 4 Vedas. Vedic epoch is a misleading term as Vedas themselves were written in stages. Looking at the astronomical evidences and hints in Vedas, we can safely conclude that they were composed after uniform intervals of about 1500 years. The sociology goes on getting more and more complex down the time line. Aryans and non-Aryan concepts slowly start segregating as we start reading Rigveda.
The key element in Vedic epoch is that it is not a HINDU History. It is more of a diary of records written in various intervals of time.
The Concept of India and all-encompassing philosophy of Hinduism slowly goes on blooming as we read through the pages of Rigveda.
Unique characteristics of Indians in Vedic epoch of Indian history are as follows.
1) Highly observant group of people. Have made many startling observations that put the discoveries of western astronomy to shame.
2) Irrespective of the genetic ethnicity, which is highly debated, the community was more aggressive initially. But with time it mellowed down.
3) Discovery the characteristic social hierarchy that has been the trademark of Indian society because of its institution. What is impressive is the social flexibility in this Varna-institution in Vedic and, to a bit lesser extent, in Puranic epoch.
Few verses in Rigveda indeed suggest the days being 6 months long. These verses are taken by AIT advocates to explain the invasion pattern. But nowhere in Rigveda are arctic flora and fauna mentioned. Rigveda remains very much Indian in composition. Yet existence of such verses in Rigveda do elicit doubts. Any addition to Vedic literature was subjected to stringent peer-review. Since the Vedas were passed on orally, the volume was kept optimum by the means of constant review. These verses may make sense simply because they were important at the time when they were incorporated in Vedas. Had they been nonsensical, then they would not have been present Vedas. OTOH, had they been truth, they would not have been found in isolation. This enigma needs to be studied thoroughly.
The War of Ten Kings - DashaRaadnya Yuddha
The first war mentioned in the Indian history belongs to Vedic epoch.
It is famously called Dasha-Raagnya Yuddha. Dasha- ten. Ragnya-Kings. War of Ten Kings.
It is extensively discussed in 7th mandala of Rigveda.
It elaborately describes the prevailing political scenario. The alliance of ten kings which invaded Bharatas and Sudas was in fact a confederation of Vedic and Non Vedic people. The tribes like Anus (Yavans??), Bhrigus (descendents of Varuna), Parthas, Purus, were all Vedic Aryans in origin. Whereas Pakhtas, Bhalanas, Dasyus, were all nonvedic in origin.
Bhalans were the tribes near Kabul and Bolan Pass. Pakhtas were Supposedly Pathans. The name Pakhtunistan suggests this possibility. Purus were residents of Sapta-Sindhu region.
The dasyus are of particular interest. Either they were Iranian counterparts of Aryans OR they were Scythians. Although Scythians never existed in such antiquity, the reason of this speculation is the term Dahae Scythiae is used by historians to describe Scythians in modern Turkmenistan. But in all probability, Dasyus OR Dahyus OR Dahae formed one of the most important part of invading force. Given the long standing animosity between Vedics and Dasyus, it is quite possible.
Anyways, to make long story short, Few Vedic kings/clans allied with non-Vedic tribes to defeat Sudas and Purus. The invading force was goaded by Vishwamitra, the famous King who later bacame a famous sage and the composer of Gayatri Mantra.
The proper battle took place on the western banks of Parusni OR Ravi River in Punjab. The accounts in Mandala 7 hymn 18 suggests that in initial engagements Sudas's army was defeated. However, they knew their country better than the invaders. They found place to safely cross the Ravi River and come on the eastern shores. The invaders, however, found it difficult to cross the river. Indra and Varuna helped Sudas to won over ten kings.
In my conclusion, there were some untimely heavy rains which disrupted the formations of invading army. Verses mention river destroying invaders by the orders of Indra. Whatever the case, army of ten kings was destroyed during their attempt to cross the river while pursuing the fleeing army of Sudas. The commander of invading army Bheda was slain by Sudas himself.
In 7.18.19, it says that Yamuna and Trutsus came to the aid of Indra. Since Indra is god of rains, it can help OR can be helped by the means of Water and Wind. Waters of Yamuna coming to Aid Indra in Punjab is highly unlikely today. But if we accept the presence of Saraswati in between Ganga and Sindhu, the guess becomes more believable.
This battle is given place in Rigveda because of its improbability of result. Franky, not even the composers of these verses expected Sudas to win. His victory is termed as victory of Deer over Lion in 7.18.17..
The aftermaths of the battle were as usual. Sudas got the booty from conquered. The distant tribes promised to pay regular tributes. Sapta-Sindhu and Aryavarta came under the dominion of Bharatas. Perhaps this was the beginning of Indian Empire. Which later came to be known as Bharat-varsha OR Bharat after the king OR clan which unified it.