One wonders, how would a French military leader like Napoleon Bonaparte be acquainted with Hussain (A.S) and his sacrifice? The answer too lies in the history of the sub-continent.
According to parhlo.com, the French and British were arch rivals when the Mughal Sultanate was on downfall. The War of Austrian Succession had broken out, which entered the sub-continent as well, the French and British fought on opposite sides. The war carried on for several years, with treaties and closings, breaking out again. The struggle for power involved native princes of India as well.
To overthrow the English government in India, French leader Napoleon had allied with the British’s worst enemies in India. A father and son known as Hyder Ali and Tipu Sultan of Mysore.
Hyder Ali was a staunch Shia and an avid follower of Hussain (A.S). When Napoleon and Hyder became allies, they used to write each other letters; exchange intelligence, war strategies, poetry, culture and even their idols. It can easily be concluded that it was through and because of Hyder Ali of Mysore and later on his son Tipu Sultan that Napoleon admired Imam Hussain (A.S) so much.
There even have been claims that before battle, Napoleon used to narrate the story of Karbala and Imam Hussain (A.S) to his army. However, no credible proof for this claim came upon research.