The Imperial lands have their origins in the conquests of Charles the Great, Charlemagne. Over 700 years ago, he conquered all of Christian Europe. With this, he won the Pope's recognition as the heir to the vacant Roman title and the stature of the secular defender of the faith. The origins of his empire lay in the old Frankish kingdoms, the remnants of those which brought about Rome's fall. His Grandfather, Charles Martel, "the Hammer", turned back the forces of Islam at Europe's southern border and took by force the crown from the moribund and weak Merovingian house. Charlemagne too, with Christendom subdued and united, campaigned tirelessly against the Moslems. However, upon his death, Charlemagne's empire fragmented, divided between three warring sons.
One son retained the imperial dignity and the old Germanic lands first taken by Charles Martel. In the next centuries, Christendom marched slowly east and north, first with missionaries, then followed by crusaders and finally colonists. The original heartland of the Empire had been the rich valley of the Rhine, then colonisation extended past the Elbe, then further past the Oder and into the Baltic, spearheaded by the Teutonic Order. In time, these new lands became stable and settled, even the formerly pagan territories of Lithuania and Hungary eventually Christianised, leaving the rich German heartland surrounded by Christian states.
The Empire bears little resemblance to the solid order of ancient Rome. Rather, the great lords are heirs to freedom loving Germanic chieftains and their kingship is an elected one. Many concessions have always had to be made by any who would assume the title "King of the Romans" and the right to journey to Rome and be crowned Emperor by the Pope. A long history of struggle, alliances and payoffs between Emperors, their great lords and the Papacy has left the lands of the Empire a patchwork of scattered possessions. The greatest lords, the seven Electors, are all but kings themselves (one of the Electors is actually King of Bohemia) and they can use their power to both elect and even depose Emperors to build their personal "empires".