Excerpts from Books and Wikipedia
"On January 10, 1356, Emperor Charles IV of Luxembourg (r.1346-1378) summoned the German princes to a diet to propose new procedures to elect the Holy Roman Emperor. . . . At this time four rival families of German princes (the Wittelsbachs of Bavaria, the Luxemburgs, the Wittenbergs of Saxony, and the Habsburgs of Austria) contested control of the imperial elections among themselves. . . .He wanted to strengthen the position of his own family by naming seven elector princes: . . . The elections would take place in Frankfurt-am-Main, and the candidate who received a majority of votes would exercise full royal authority straightaway, so ending the pope's role. . . . These arrangements, with the later addition of Bavaria and Hanover to the number of elector-princes, would govern the election of the Holy Roman Emperor for the next four centuries." [Furtado: 1001 Days]