Around 1100 AD, the Mamluks who had already conquered Persia (modern Iran) came to conquer India as well. By 1192 AD, the Mamluks were able to beat the Rajput kings of India and take over northern India (and modern Pakistan).
In 1192 AD, the Muslim general Muhammed Ghor captured Delhi and started a dynasty of rulers which, together with some later dynasties, is called the Delhi Sultanate. The first dynasty was called the Slave Dynasty because the first leaders had been slave soldiers, or Mamluks Little by little, many Hindus and Buddhists in northern India decided to convert to Islam, the religion of their conquerors..
When the Slave Dynasty ended in civil war in 1290, the Khalji Dynasty took over. This was the time of the greatest power of the Delhi Sultanate, when the Sultans in Delhi could control even the most southern part of India, at least some of the time.
Tomb of a Tughluq sultan
Under the Tughluq Dynasty, however, beginning about 1325, the Delhi Sultans began to weaken. There were a lot of rebellions and civil wars, and by 1351 southern India regained its independence as a Hindu state. The Deccan, or central India, also broke away and became independent, although as an Islamic state.
In the end, Delhi was sacked by the Mongol invader Tamerlane or Timur in 1398, which pretty much ended the power of the Delhi Sultanate.