Germany
The Imperial Crown
How much of this did the Emperor actually rule? Almost none. In the Empire as in other kingdoms, the idea was that the monarch should "rule of his own," meaning that he had his own family estates, plus estates belonging to the crown, and that these provided his income and his army—everything he should need. Only in special circumstances (e.g., a crusade) did the lands over which he ruled need to contribute, and even then it should be voluntary.
If the imperial crown stayed in one family for a long time, then that family could gradually accumulate a preponderance of land and titles, making them more powerful than anyone else in the Empire. This is what happened with the Capetians in France and the Plantagenets in England. It nearly happened with the 
Hohenstaufen in Germany, but a crisis in the 13th century ended that dynasty (more about that later). Consequently, by 1300, the imperial crown and even the German crown had very little of its own sources of income and very few men it could
directly command. It did, however, continue to have a tremendous amount of prestige, making it an object of ambition.
The situation in 1300, therefore, was complex. I'll describe the dynastic woes in the following pages. Here I wish to emphasize Germany was the least centralized and least powerful of medieval monarchies on a day-to-day basis, though if all of its various lands contributed in full measure it could command greater resources than anyone. It just never happened, is all.
But the French monarchy nearly fell apart in the late Middle Ages, and so did the English monarchy. There was no intrinsic reason why the German monarchy couldn't have gained strength and centralized. It didn't, though, and why it didn't forms one thread in the narrative that follows.
The other point I wish to emphasize here is that the parts of the Empire are more important than their sum. I'll be concentrating on the imperial narrative for the sake of simplicity (though you won't think it
simple!), but what we really should be doing is following a half-dozen narratives at once: Bohemia, Luxemburg, Brandenburg, Bavaria, the Palatinate, and so on, not to mention Burgundy or Prussia or the Hanseatic League. Along with them we should follow another dozen individual powerful cities such as Cologne or Augsburg. The Empire was much more a conglomeration of these powers than it was an entity unto itself.
Whereas I begin with 1300 or even a little later in our other political narratives, for the Empire I begin much earlier. For no discussion of the late medieval Empire can omit a consideration of the end of the House of Hohenstaufen.