What was the main theme of the novel 'neel darpan' which aroused spirit of nationalism in India?

Exploitation of Indian farmers.

Explanation:

Written in the year 1858-59 by Dinabandhu Mitra, Nil Darpan is a Bengali play. It was published in the year 1860 in Dhaka. The theme of this play is the exploitation of the Indigo workers, their situation and many dimensions of their situation varying from social, physical, psychological and economic, to cruelties of in humanism. Accordingly, when Indian people read this play they realized the British government should not exploit Indian farmers and thus it gave a boost against the colonial empire.