Around 1100 AD, with the Ghaznavids out of the picture, the Mamluks who had already conquered Iran and what is now Pakistan succeeded in conquering the rest of northern India as well, uniting a rich kingdom that was the center of the Silk Road. In 1192 AD, the Muslim general Muhammed Ghor finally captured Delhi from the Rajput kings of India and started a dynasty of rulers which, together with some later dynasties, we call the Delhi Sultanate. The first dynasty was called the Slave Dynasty because the first leaders had been enslaved soldiers, or Mamluks. Little by little, many Hindus and Buddhists in northern India decided to convert to Islam, the religion of their conquerors.
In the last years of the Slave Dynasty, the Mongols invaded Pakistan. They soon had a lot of influence over the rest of northern India, but they never formally took it over.
When the Slave Dynasty ended in civil war in 1290, the Khalji Dynasty took over. They pushed the Mongols out of India with several big victories. This was the time of the greatest power of the Delhi Sultanate, when the Sultans in Delhi could reach even the most southern part of India, at least some of the time. In 1311, a successful plundering invasion captured the Pandya king, Sundara Pandyan, and destroyed several Hindu temples. The Pandyas had to pay huge amounts of gold and pearls to get their king back.
Under the Tughluq Dynasty, however, beginning about 1325, the Delhi Sultans began to weaken. There were a lot of rebellions and civil wars – possibly the bubonic plague played a part, together with the collapse of the Mongol Empire – and by 1351 southern India regained its independence as a Hindu state under the Vijayanagara Empire. The Deccan, or central India, also broke away and became independent, although as an Islamic state.
When the bubonic plague was over, the Mongol khan Timur tried to recreate the Mongol Empire. In 1398, he sacked Delhi – he wrecked it – which pretty much ended the power of the Delhi Sultanate. But his empire paved the way for the Mughal Empire that came after it.