Attacks by Mongols and others
Mongols were nomadic groups who inhabited the steppes north of China and east of Lake Baikal.
They formed a huge nomadic empire under Chengiz Khan in the 12th century.
From 13th century onwards they repeatedly attacked the Delhi Sultanate.
A lot of energy and resources of the Sultans were spent in facing these invasions but they could not destroy the sultanate.
The weakness of the Delhi Sultanate was made even worse by Timur’s invasion of Delhi (1398).
Timur was a son of the Chief of Chagtai branch of Turks.
When he invaded India he was the master of almost whole of Central Asia.
Sultan Nasiruddin and his Wazir Mallu Iqbasl faced Timur but were defeated.
Delhi Sultanate lost control over Punjab.
Timur appointed Khizr Khan, the ruler for Multan who controlled Punjab also.
After the fall of Tughlaq dynasty Khizr Khan occupied Delhi and became the ruler of Delhi Sultanate. He laid the foundation of Saiyyid Dynasty.
 Inner Conflict of Nobility
Delhi Sultanate witnessed five dynasties ruling over it.
The main reason for change of dynasties and deposing of rulers was a constant struggle between the Sultan and the nobility (Umara).
 Provincial Kingdoms
Another consequence of this conflict was declaration of independence by various provincial heads in the regions.
As a result a number of independent Afghan and Turkish kingdoms emerged.
Important ones of such states were Bengal (Lakhnouti), Jaunpur, Malwa, Gujarat, the Bahmani kingdom in the Deccan etc.
The whole process weakened the sultanate.
 Resistance by Indian Chiefs
The sultans had to face the resistance from Indian chiefs at regular intervals.
The Rajput chiefs in Rajputana (Mewar, Ranthambhor, Chittor etc.), Warangal, Deogiri & Ma’bar in Deccan and South, the king of Dhar, Malwa in Central India, Jajnagar in Orissa and a host of smaller chieftains were constantly at war even after successive defeats.
All these struggles weakened the sultanate.
The Delhi sultanate was considerably weakened after the Khalji and Tughlaq reign.
Finally the invasion of Babur in AD 1526 brought it to an end.
 Rise of The Provincial Kingdoms
These kingdoms were Jaunpur, Kashmir, Malwa, Gujarat and Bengal.