Prayers for the Holy Roman Emperor figured in all Christian (Catholic) missals and, until recently, were recited on Good Friday and Holy Saturday. The election of an emperor (who originally had to be crowned by the pope) became a feast all over western Christendom. In American Catholic missals these prayers appeared until World War II, when they were formally abolished by Pope Pius XII. Such prayers were also recited in Lutheran services, and in Prussia they were cancelled only upon the orders of Frederick II in the eighteenth century… He [the Emperor] was chosen by the electors, and before his coronation he had the title “King of the Romans.”  (The seven, eight, or nine electors were powerful princes, secular or ecclesiastical.) After Frederick III (1440-1493) it became inconceivable that any other but a Habsburg could be elected… as successor of the Caesars, surrounded by the glory of universality: the Pope was the spiritual, the Holy Roman Emperor the temporal head of the world. 

-Erik Ritter von Kuehnelt-Leddihn, The Intelligent American’s Guide to Europe