The Mughals did not have a law of 'primogeniture' i.e., a law, whereby, the first-born son would naturally inherit the throne. Hence, every time a king died, there was a war of succession among the contenders to the throne. After Aurangzeb's death, the last of the great Mughals, there followed a war of succession among his three sons. Consequently, a weakened leadership could not stem the rot of corruption and resultant decline.
Shah Jahan's zeal for construction had already depleted the treasury. Aurangzeb's long wars in the Deccan caused a further drain. Many zamindars, princely rulers stopped paying revenue to the empire. The continual and ever increasing demand of the peasants became unbearable and often they rose in revolt.
Invasions of Nadir Shah and Ahmed Shah Abdali and their repeated blunders not only harmed the empire financially but also shook its stability. He took away the renowned Kohinoor. After Nadir Shah's invasion, the Mughal empire shrunk in size rapidly.
Weak successors of Mughal empire
The successors of Aurangzeb were very weak. They could not check the disintegration of the empire.The absence of the law of primogeniture was another cause for the downfall of the empire. After the death of each Mughal emperor, there was a war of succession among his sons and it paved the way for their own downfall.
Aurangzeb was chiefly responsible for the disintegration of the Mughal empire. His strict religious policy, long stay in the Deccan, vastness of his empire and his suspicious nature not only ruined himself but also paved the way for the downfall of the mighty Mughal empire.
Weak military organisation and administration
As the Mughal empire became very vast, it was difficult for the Mughal rulers to control distant parts of the empire. So, revolts broke out in many parts. There was deterioration and demoralisation of the Mughal army.The soldiers cared more about their personal benefits than winning the battles.