The mughal empire was the last empire which ruled the subcontinent. It was the last [seemingly] golden age of the subcontinent. During it many monuments were built like the taj mahal, the peacock throne, badshahi mosque e.t.c which seem itregal to the indian culture. The mughals influenced the cuisine, architechture and even the language (Urdu/Hindi) which devoloped during its time. The 300 years the mughals ruled undoubtedly influenced the way India is. Just the way the mughal rule is very important to the way India is, its decline is also. Mainly because of the space left by its decline the british came. The reason of decline can be classified in three categories
which are linked together.
Ecnomic: The mughal goverment took taxes from all the country using the jagirdar nizam. The jagirdar was not paid any salary and so he took as much extra money as he wanted. There was no system to regulate the taxes and the ryots could not appeal to a higher authority after Shan Jehan distanced himself from the people. However the was no system to protect the ryots. The primary reason of the goverment was to provide protection to the peasents from oppression. However the goverment after the maratha insurgence failed to protect them and because the raiders took away the product of their labour they abandoned agriculture altogether and either migrated to the city or themselves became raiders.This caused loss in revenue and also caused prices to rise ruining both mughals and also the normal people. Another reason was that the mughals wasted all there money in useless products like the taj mahal and the peacock throne instead of using it on education, sciences, hospitals and agricultural and arms research.
Millatry: The mughal army was supreme because it was in the indian peninsula rather than in the central asia or europe. The tactics were outdated and the army relied on slow elephants. Its technology was outdated and was easily defeated as shown by the mughal failure to capture Kandhar. When the army moved a whole city moved with them. There was no discipline in the army and the soldiers fought in an unorgaanized way. The mobility of the army was zero. Without a functioning army the empire could not remain.
Political/Administrative: There was no uniform law in the empire and the king was above the law as well as the source of law. Justice was at the whim of the king. The power of the emperor was only in the capital, outside the will of amirs prevailed. After Shivaji ther marathas caused the law and order situation to detoriate by raids. There was also no police and no force to protect them.
These are the main reasons of the decline of the empire.