 Upon his accession to the imperial throne , Joseph ruled less land than his father had in 1740 . Believing that the emperor must possess enough land to maintain the Empire 's integrity , Maria Theresa , who was used to being assisted in the administration of her vast realms , declared Joseph to be her new co @-@ ruler on 17 September 1765 . From then on , mother and son had frequent ideological disagreements . The 22 million gulden that Joseph inherited from his father was injected into the treasury . Maria Theresa had another loss in February 1766 when Haugwitz died . She gave her son absolute control over the military following the death of Count Leopold Joseph von Daun . 
