Answer:
The invasion of northern India by Muslim rulers in the late 1100s was successful because Hindu princes wasted resources battling one another instead of uniting against a common enemy, Option D.
Explanation:
Muslims rulers won on the battlefield because Muslim warriors arched quicker than the Hindu forces who rode slow-moving war elephants. Hindus wasted resources battling each other.
During that time, Hindus had highly influenced social structure, so people from lower caste were not treated well by the high-class people. So, Hindus were divided and fought with each other. This led to successful invasion of Muslim rulers in late 1100s. Many low-caste Hindus converted themselves to Islam in many places.