The Delhi Sultanate deserves to be considered an all-India empire.  

• Virtually all of India, except Kashmir and Kerala at the far ends of the subcontinent, and a few small tracts in between them had come under the direct rule of Delhi towards the close of Muhammad bin Tughlaq’s rule.  
• There were no well-defined and accepted rules of royal succession and therefore contested succession became the norm during the Sultanate.  
• The Sultans required the holders of iqta’s (called muqtis or walis) to maintain troops for royal service out of the taxes collected by them.  

• Certain areas were retained by the Sultans under their direct control (khalisa).  
• It was out of the revenue collected from such areas that they paid the officers and soldiers of the sultan’s own troops (hashm-i qalb). 

Source: Tamil Nadu state board.