In the crisis that broke out in 1866 around the supremacy of Prussia or Austria in the German Federation, as Hannover refused to support Prussia's plans of reform and also afforded no consequence to an ultimatum, it was occupied by Prussian troops. In a proclamation from June 19, 1866, the commanding general V. Falckenstein ordered that "The administration of the kingdom from now on passes to me", and he commanded further from his headquarters in Hannover that "the administration in all sectors will carry on unchanged according to the Royal Hannoverian laws and regulations and all public officials will remain in their posts." At the end of July, the Prussian king appointed a governer-general of the Hannover Kingdom; but the hoped-for peace agreement failed to materialize. Instead, the former Hannoverian kingdom was, through a Prussian Annexation Patent of October 3, 1866, incorporated as a province in Prussian territory.

In the organization of the government administration, for the time being, no changes occurred, The governor-general only decreed on October 30, that the public authorities henceforth shall take on the Prussian Royal designation.