The Ghūrids

After Mahmūd, the Ghaznavid Empire was attacked from all sides and soon fell apart. The chiefs of Ghūr, a mountainous region of Afghanistan west of Ghazni, had been Ghaznavid vassals. They seized Ghazni and built up their own power.

Their leader Muhammad, sultan of Ghūr (Muhammad Ghūrī), soon took parts of Punjab and Sindh. But his attempt to enter Gujarat failed: in 1178 he was defeated by the Chaulukya king Mūlarāja II at the foot of Mount Abu. Another version says it was Queen Nāīkīdevī, Mūlarāja's mother, who led the army on horseback with her young son on her lap. Historians are divided over who should get the credit, but all sources agree Muhammad was defeated there.

Meanwhile the Chāhamānas (Chauhāns), a powerful Rajput dynasty, conquered Delhi, Haryana, parts of Punjab and Uttar Pradesh, and most of Rajasthan in the 12th century, with their capital at Ajayameru (today's Ajmer). Their inscriptions call Delhi 'Dhillikā', later shortened to 'Dhilli' and finally 'Delhi'.

In 1191, the Chāhamāna king Pṛithvīrāja III defeated Muhammad Ghūrī at Tarain. But within a year Muhammad returned with a bigger army. In the Second Battle of Tarain (1192), after fierce fighting, he defeated Pṛithvīrāja and had him executed.

Muhammad Ghūrī then captured Delhi. Unlike Mahmūd, who plundered and went home, Muhammad wanted to keep the land. He returned to Ghazni but left trusted commanders behind — above all Qutb-ud-din Aibak, who later founded the Delhi Sultanate. That difference is what makes these centuries a turning point.

His commander Bakhtiyār Khiljī campaigned in eastern India from the end of the 12th century, conquering Bihar and Bengal. On the way he destroyed great Buddhist monasteries and universities, including Nālandā and Vikramaśhilā, taking huge booty and killing many monks. Historians of Buddhism agree that losing these great centres of learning sped up the decline of Buddhism in India.

Nālandā's famous library, in three tall buildings, held lakhs of manuscripts; after the attack it is said to have burned for months. Tibetan scholars who taught and studied there fled home carrying as many manuscripts as they could. About thirty years later, a Tibetan monk, Dharmasvāmin, found Nālandā half in ruins — yet a 90-year-old teacher, Rāhula Śhrībhadra, was still teaching a class of about 70 students. Perhaps Nālandā's last class.

Around 1203–04, Bakhtiyār surprised the Sena ruler at Nādīya, then tried to invade Tibet. But passing through Kāmarūpa (Assam) in 1205, his army was badly beaten by the local ruler's forces. The people are said to have destroyed food and fodder, starving the invaders; Bakhtiyār escaped with only a handful of men. In 1206 Muhammad Ghūrī was killed, and the same year Bakhtiyār was killed, apparently by his own men.