In his amusing article in the New York Times, Adam Goodheart records ten dates which changed history (of the US!). His entry for 19 April is delightfully Napoleonic.
“APRIL 19, 1802: Mosquitos Win the West
Events that change America don't always occur within our borders. Consider the spring of 1802. Napoleon had sent a formidable army under his brother-in-law, General Charles Leclerc, to quell the rebellion of former slaves in Haiti.
On April 19, Leclerc reported to Napoleon that the rainy season had arrived, and his troops were falling ill. By the end of the year, almost the whole French force, including Leclerc himself, were dead of mosquito-borne yellow fever.”
“10 Days That Changed History”, New York Times, 2 July, 06 by Adam Goodheart