One of the major powers in Europe during the 13th century. It contended with the Papal States for the controlling influence over the rest of Europe. Its borders stayed largely static throughout the middle ages and onwards because of the deep rifts between the different duchies. The emperor often spent the entirety of his reign preventing civil war between these semi-autonomous states, and the death of an emperor often precipitated a minor civil war while factions tried to get 'their guy' on top. At the time of the Mongoliad, the Empire was at the peak of its power and influence under Frederick II, contending with the Papacy and the Kingdom of Sicily for power in Italy.

It's worth noting that the Teutonic Knights, historic antagonists of the OMVI, were based in the Holy Roman Empire, and at the time gave their support to Emperor Frederick II. It is probably safe to assume that the Shield-Bearers were not on good terms with either the Knights or the Empire.