Political map of Europe & the Mediterranean 14 June 1866 (Outbreak of the Austro-Prussian War): After the war with Denmark (Second Schleswig War), Austria and Prussia were left in control of Schleswig-Holstein (Schleswig-Holstein Question). However the Prussian Prime Minister Otto von Bismarck (Otto von Bismarck) really wanted both duchies and connived to provoke a war with Austria (Gastein Convention). Most of the German states backed Austria, voting for mobilization against Prussia (Austro-Prussian War) in the German Federal Diet (Federal Convention (German Confederation)).