The Battle of Plassey: The officials of the Company made rampant misuse of its trade privileges that adversely affected the nawab’s finances. The English fortified Calcutta without the nawab’s permission.  

• The Company further tried to mislead him, and compounded their sin by giving asylum to a political fugitive, Krishna Das, son of Raj Ballabh who had fled with immense treasures against the nawab’s will.  
• The Company, on its part, suspected that Siraj would drastically reduce its trade privileges in collusion with the French in Bengal.  
• Thus, when Siraj attacked and seized the English fort at Calcutta, it brought their hostility into the open. Mention may be made here of the much propagated ‘Black Hole Tragedy’.  

• Siraj-ud-daula is believed to have imprisoned 146 English persons who were lodged in a very tiny room due to which 123 of them died of suffocation.  
• However, historians either do not believe this story, or say that the number of victims must have been much smaller. 

Source: Spectrum’s A Brief History of Modern India.