This section is from the book "Some Contributions Of South India To Indian Culture", by S. Krishnaswami Aiyangar. Also available from Amazon: Some Contributions of South India to Indian Culture.
It is well-known that the Mahammadan irruption this side of the Vindhyas commenced in the last years of the thirteenth century, under the Khilji ruler Alau-d-din, and that it began as a mere raid for purposes of plunder. Once Alaud-din obtained a considerable amount of wealth that served him the useful purpose of paving the way to the throne. He often had occasion to look out to this source of revenue to fill his treasury even when he had placed himself firmly upon the throne. Alau-d-din's needs were great as the main purpose of his reign was to keep the Moghals out of the North-Western frontier. If the Mahammadan historian Wassaf speaks the truth, and there is nothing to doubt his veracity in this particular, Alau-d-din had to maintain a standing army of 475,000 at a cost of 180 dinars a month each man, and 230 for each horse; he even allowed a spare horse to a soldier, and to those who maintained a second animal he gave an additional allowance of this amount. One could understand therefore that the demands of the military department of Alau-d-din's reign were more than the ordinary revenues could meet. He therefore adopted the prudent policy in respect of South India by making an impression upon the Hindu rulers of his own great power and putting these Hindu rulers under heavy tribute. Such in fact were the instructions that he actually gave to the generals he deputed on these several invasions, as recorded by Amir Khusru.
In the carrying out of these instructions the generals had a great deal left to their own discretion, and these invasions generally meant a considerable volume of destructive work. The first object of these generals was to take possession of what was termed "royal wealth." This consisted in what in modern parlance would be called materials of war, not necessarily contraband of war, and included elephants as the first item, horses, gold and jewels, and other commodities of value that could be carried off easily. The royal treasuries were one source; and the generals soon found the temple treasuries equally fruitful as a source of revenue. The armies sent out could not be very large having regard to the distance, which in the language of the Mahammadan historians were six months' jour-ney and twelve months' journey. They consisted merely of picked cavalry, and had, as a military necessity, to carry on the war on a more destructive method than would otherwise. have been necessary. Hence to the South Indian, Mahammadan invasions meant destruction of all the cherished wealth of the people. One specific instance of such destruction recorded by the Mahammadan historians is the destruction of fruitful trees, which sometimes were cut down by the thirty thousand, to the great horror of the Hindus. Naturally therefore these invasions of the Mahammadans extending over a period of about thirty years struck the Hindus of the south with consternation and terror to such an extent that they felt it necessary very early to organise themselves for fighting for their existence. This organisation found its leader in the Hoysala ruler of Mysore at the time, Vira Ballala III. Almost after the first raid upon his capital -by Malik-Kafur, he understood what the Mahammadan invasions meant and as a consequence he adopted a temporising policy. Till his contemporaries should be of a temper to act together as against this common enemy, he entered into terms of treaty with Alau-d-din, and kept up to the terms of the treaty as long as he found it necessary to do so. But fortunately for him, the death of Alau-d-din created such a series of disturbances in Delhi, and, thanks to the exertion of Alau-d-din, the Moghal troubles ceased to be imminent. The Hoysala had found time to organise his forces and put himself in a position of readiness for eventualities. He slowly set about reorganising his own resources and leaving his neighbours to do what they thought best in the circumstances for them-selves; so much so, that, when Mubarak organised a South Indian Province for the Mahammadans with Deogir as its capital the Hoysala showed no activity outside of his frontier even when garrisons of Mahammadans were planted quite on his northern frontier. It is when Mahammad-bin-Tughlak placed himself upon the throne and undertook his invasion of the South, that the time had come for a Hindu organisation of the South Indian rulers, and that was brought about by the Hoysalas with the co-operation of the contemporary Kakatiya ruler.
In the meanwhile the Mahammadan garrisons left by Malik-Kafur had been dislodged from the Tamil country by the Kerala ruler, Ravivarman Kulasiklara, who broke out of his mountain frontier and carried his armies successfully as far as Poonamallee, perhaps only to retire, when the Kakatiya general advanced against him. The Tamil powers having become powerless or practically extinct, it was left to the Kakatlyas and the Hoysalas to do the work of organising a successful resistance. This was made the more necessary, when Mahammad undertook another invasion to re-assert his authority in South India and locate a permanent garrison in Madura. This was done successfully, and the South was held in the interests of Mahammad for a period of about seven years by the successive governors sent out to Madura. A rebellion set up early in the reign by his cousin Bahau-d-din at Sagar gave the signal for other rebellions, and the establishment of a Mahammadan sultanate at Madura by Mahammad's own governor provoked the Hoysala and the Kakatiya rulers to join their resources and make a stand for themselves. A too early rising would have put them between two fires, Mahammad's province of Deogir in the north and the Mahammadan Sultanate in the South. But Mahammad, with his wonted imprudence, involved himself in a sea of trouble nearer his headquarters, and that engaged him fully. The two high powers of the south were left to watch the northern frontiers and carry on a campaign to destroy the Mahammadan garrisons in the South including that at Madura. The latter portion of the work fell upon Vira Ba]]ala himself who since A.D. 1328, the year of Mahammad's last invasion of the south made Tiruvannamalai his capital, and was carrying on a systematic campaign against the Sultanate at Madura. The northern frontier was left in charge of a number of generals of whom three happened to be brothers. They held the frontiers successfully against the Mahammadans, and this frontier extended from the west coast, somewhere a little north of Goa, right across to the mouth of the river Krishna. The flank of the Mahammadan province of Deogir was watched by the Kakatiyas, nominally under tribute to Mahammad. The Hoysala was therefore able to carry on war in the south unmolested by any action of Mahammad. He fell in the fight however about the end of the year 1342, and his son followed after a short rule of about two to three years.
In the meanwhile Mahammad involved himself inextricably and died in the course of the next five or six years. His death was the signal for the generals of the Hoysalas to carry out the policy of their late master to a successful termination, and it is to a son of one of the brothers who held the northern frontier to whom is due the credit of having destroyed the Mahammadan Sultanate of Madura.
This war takes on the character of a patriotic struggle by the Hindus for mere existence and for the preservation of all that was cherished as sacred from the point of view of religion, and all that was worth having by way of secular resources. This aspect of the movement it was, that gave it its peculiar character and culminated in the foundation of Vijayanagar. Vijayanagar stood forth as the visible embodiment of the national resistance to save this enclave for the Hindus and keep it free from being over-run by the Mahammadans.