How did Hyderabad become part of India?

Hyderabad became a part of India following Operation Polo in September 1948. It was a military operation in which the Indian Armed Forces invaded the Nizam-ruled princely state, merging into the Indian Union.

The reason that led to India undertaking Operation Polo was that it could not let a state as vast and as rich as Hyderabad to continue as an independent entity, for fears that it would lead to further demands of independence from other states that were incorporated recently

For further reading check the following articles:

• Prehistoric Age in India
• Portuguese India
• Prehistoric Rock Paintings