 After a series of perceived provocations from Prussia , culminating in the offer of the Spanish crown to the Prussian Prince Leopold of Hohenzollern , the French emperor Napoleon III declared war on 15 July 1870 . Initially this step was supported by an outbreak of patriotic fervour and confident expectations of victory . Bizet , along with other composers and artists , joined the National Guard and began training . He was critical of the antiquated equipment with which he was supposed to fight ; his unit 's guns , he said , were more dangerous to themselves than to the enemy . The national mood was soon depressed by news of successive reverses ; at Sedan on 2 September the French armies suffered an overwhelming defeat ; Napoleon was captured and deposed , and the Second Empire came to a sudden end . 
