What caused famine in Bengal during British rule?

The objective of Nehru’s forward policy was to force the Chinese from territories claimed by the Indian government. 

Nehru’s forward policy did not achieve what he had wanted. Contrary to his predictions, China attacked Indian outposts north of the McMahon Line. Thus began the Sino-Indian War that ended in Indian defeat after 30 days of fighting

For further reading check the following articles:

• First and Second Anglo-Mysore War
• Battle of Porto Novo
• European Colonialism