The war erupted as a result of the dispute between Prussia and Austria over the administration of Schleswig-Holstein, which the two of them had conquered from Denmark and agreed to jointly occupy at the end of the Second Schleswig War in 1864. The crisis started on 26 January 1866, when Prussia protested the decision of the Austrian Governor of Holstein to permit the estates of the duchies to call up a united assembly, declaring the Austrian decision a breach of the principle of joint sovereignty. Austria replied on 7 February, asserting that its decision did not infringe on Prussia's rights in the duchies. In March 1866, Austria reinforced its troops along its frontier with Prussia. Prussia responded with a partial mobilization of five divisions on 28 March.