The causes which led to the downfall of Tughluq dynasty are:- 1. The Annexation of the South 2. The Failures of Muhammad Tughluq 3. The Weaknesses of Firuz Tughluq 4. Incompetence of the Successors of Firuz 5. The Incompetence and Demoralization of the Nobility 6. Invasion of Timur.
Cause # 1. The Annexation of the South:
Ghiyas-ud-din Tughluq adopted the policy of annexing the conquered territories of the South. Muhammad Tughluq led it to perfection. But this policy proved against the permanent interest of their empire. Due to lack of proper means of communication and transport, it had been always difficult for every emperor of the North to keep the South under his control for long.
India could not be united under one rule till modern times during the period of the British when means of communication and transport became well-developed. That remained the fact in case of the Tughluqs also.
The South became independent during the later period of Muhammad Tughluq who himself had been primarily responsible for its conquest. Thus, the conquest of the South by the Tughluqs brought no advantage to them. On the contrary, it adversely affected the resources and the strength of the empire.
Cause # 2. The Failures of Muhammad Tughluq:
Muhammad Tughluq failed both in his foreign and internal policy. While Bengal and the South regained independence and the hold of the Delhi Sultanate became weak over Gujarat and Sind, no significant territory could be added to the empire permanently. The same way, all his schemes of reform failed miserably and brought economic ruin to the empire.
Besides, his policies and severe measures resulted in widespread revolts at different places which taxed further the energy and resources of the empire. Muhammad Tughluq, thus, failed to protect and consolidate even that empire which he had inherited from his father. He bequeathed to Firuz a shrinking and bankrupt empire. Therefore, Muhammad Tughluq was largely responsible for the downfall of his dynasty.
Cause # 3. The Weaknesses of Firuz Tughluq:
Firuz, no doubt, succeeded in restoring economic prosperity to the empire and did many useful works of public welfare. But, his imprudent generosity, laxity in administration, slave- system, policy of intolerance towards the Hindus, restoration of the prestige and influence of the Ulema in matters of the state and neglect to build up military strength of the empire went against the permanent interests of the state. Firuz, in fact, failed to restore the prestige and power of the Delhi Sultanate which alone could provide it longer life.
Cause # 4. Incompetence of the Successors of Firuz:
Among the successors of Firuz, in fact, no one deserved to be the Sultan of Delhi. Firuz died at a ripe age of nearly 80 years and his two elder sons, who could be competent, died during his life-time. His third son Muhammed was a pleasure-seeker and therefore, was devoid of his right to the throne.
Firuz nominated Tughluq Shah, son of his late eldest son as his successor. Prince Muhammad fought both against Tughluq Shah and his successor Abu Bakr. He succeeded but conflicts between royal princes gave chance to nobles at the court and governors of provinces to increase their power and influence at the cost of successive Sultans.
Thus, later Tughluqs proved incompetent and ineffective in matters of the state and Sultan Nasir-ud-din Mahmud, the last ruler of the dynasty met an ignoble death. During medieval age, the fate of the state was largely determined by the character, personality and military strength of the Sultan. The incompetence of later Tughluqs, therefore, was certainly very much responsible for the downfall of the empire.
Cause # 5. The Incompetence and Demoralization of the Nobility:
Nobles and provincial governors of later Tughluqs took advantage of incompetence of their rulers. Those who were ambitious and competent established independent kingdoms out of the ruins of the empire and those who were incompetent stuck to the court engaging themselves in corruption and luxuries. None of them proved competent and whosoever was competent was disloyal to the Sultan and therefore, worked against the interest of the Delhi Sultanate.
Cause # 6. Invasion of Timur:
Timur gave final blow to the power and prestige of the Tughluqs. The empire, in fact, did not exist even prior to his invasion. Timur brought this fact to glaring light.
Thus, different factors participated in bringing about the downfall of the Tughluq empire. However, its rulers were primarily responsible for it as had been the case with every empire in India and also elsewhere in the world during the medieval age. The process of disintegration started with the reign of Muhammad Tughluq; Firuz, in his own way, contributed towards this process; and, during the period of later Tughluqs it completed itself.