<P> The Franco - Prussian War or Franco - German War ( German : Deutsch - Französischer Krieg , French : Guerre franco - allemande ) , often referred to in France as the War of 1870 ( 19 July 1870 -- 10 May 1871 ) or in Germany as 70 / 71 , was a conflict between the Second French Empire of Napoleon III and the German states of the North German Confederation led by the Kingdom of Prussia . The conflict was caused by Prussian ambitions to extend German unification and French fears of the shift in the European balance of power that would result if the Prussians succeeded . Some historians argue that the Prussian chancellor Otto von Bismarck deliberately provoked a French attack in order to draw the independent southern German states -- Baden , Württemberg , Bavaria and Hesse - Darmstadt -- into an alliance with the North German Confederation dominated by Prussia , while others contend that Bismarck did not plan anything and merely exploited the circumstances as they unfolded . None , however , dispute the fact that von Bismarck must have recognized the potential for new German alliances , given the situation as a whole . </P>
why did france declare war on prussia in 1870
Prussian ambitions to extend German unification French fears of the shift in the European balance of power