In September 1805 the Electorate of Bavaria under Prince-elector Maximilian I Joseph of Wittelsbach , that had been allied Collaboration with the Habsburg Monarchy under the common federally structured Holy Roman Empire , went Change over to Napoleonic France : the Bavarian Minister Count Maximilian von Montgelas , realizing the French superiority while fearing the ambitions of the newly established Austrian Empire , signed Sign_agreement a secret defence alliance at Bogenhausen .