Access to horses was the most critical factor in the success of an empire in the medieval period. Slowly but steadily, India was colonized by foreign powers after this access to horses was cut off.
Hiuen Tsang wrote of the five regions of India (Jambu Dwīpa) of which the northern region was known as the land of the horses, where men were cruel in disposition: they divide like birds going here and there, tending to their flocks of cattle.
One fascinating thing is that in Hiuen Tsang’s time, Xinjiang region was still being referred to by its Sanskrit name “Gōsthāna” गोस्थान (pasturage), which he writes as “Kiu-sa-tanna”. That ultimately became “Khotan”. The king called himself a descendant of Kubēra (Vaiśrāvana). 
One of the names for horse in India might have come from old Tibetan or Mongol (Rmang or Mrang) as “gurram” గుర్రం in Telugu or “ghoda” घेड़ा in Hindi. This has some other links in Indo-European languages like “mare” in English. Welsh even has “gorwydd”.
languagelog.ldc.upenn.edu/nll/?p=42523
languagelog.ldc.upenn.edu/nll/?p=42523
I am thinking that different types of horses based on their breed or origin might have been called different names in Sanskrit. Hiuen Tsang mentions the regions where the prized “Shen” horses are to be found (one of them being Persia or “Polosi”, where he says were many temples).
Anyway, once India’s access to these regions with horses was cut off, capitulation to invading armies was a certainty. No Hindu empire was secure without horses, including Vijayanagara empire, which had to import horses from hostile powers and even from Europeans.
Earlier, it seems to have been a regular feature for Indian empires to periodically invade the northern “Kambhōja” and “Hūna” regions (as well as the western “Yavana” regions) and bring them under submission. Kālidāsa describes the Digvijaya of emperor Raghu in his Raghuvamśa.
Raghu first uses the power of cavalry to bring southern kingdoms to submission. Kālidāsa says the hooves of the horses dug up dust of cardamom.
Later in the north, Raghu uses elephants to bring Kambhōja into submission: the elephants were scratching on the barks of walnut trees.
Later in the north, Raghu uses elephants to bring Kambhōja into submission: the elephants were scratching on the barks of walnut trees.
Kālidāsa says the troops of Raghu enjoyed coconut wine in the south and grape wine in the west. He says the faces of Yavana dames were drunk with wine. The rich geographical variation in ancient India was thus managed by an empire, so that all resources were effectively deployed.
So when Indian empires stopped conducting Digvijaya campaigns, it was only a moment of time before the imbalance in the resources would create a collapse of the empire. This is exactly what happened in the medieval times due to the loss of horses.
