Mssr Roy said:
Eh most people consider 1648 relatively late in the breakup of the empire...I consider it when the Golden Bull was passed in 1356. Many people consider it even earlier than that. For example, the MES has the HRE breaking up in the mid-1100s.
BTW this is a 900-1200 scenario, so 1648 isn't that important a date
A very brief list of major 900-1200 Germany/HRE dates, gleaned from a couple websites:
911 Lorraine flops from east Francia (Germany) to west Francia (France).
922 the title of Emperor lapses when Burgundy captures northern Italy. (Before this the title didn't mean the same thing it meant later anyway.)
925 Lorraine goes back to east Francia
961/962 Otto conquers Italy, and claims the imperial title.
1025 With the death of the last Saxon emperor (Henry II), the process of electing emperors begins.
1032 Conrad inherits Burgundy, thus filling out the generally accepted boundaries of the empire (the "four crowns").
1075/1076/1077 The Investiture controversy - the pope essentially legalizes revolts in Germany, and indeed Saxony does revolt. According to
this website, the emperor faced challengers from Swabia, Luxembourg, and Franconia for the next 25 years.
1122 The Concordat of Worms ends the investiture controversy, but robs the emperor of most of his religious power.
1158 Frederic Barbarosa declares "the leader is not bound by law" and reclaims imperial power in the face of a stronger pope.
1220/1232 Frederick II grants the german duchies formal ownership of their land, and the rights to tax and mint coin.
I mention the last one (even though it is past the time period) because, along with the interregnum in 1254-1273, this seems to represent the end of the centralized empire. Frankly, I can't find anything to suggest a massive decentralization from 1150-1200, although the splintering that happens in the Mongol scenario seems to be backed up by solid historical events. My guess is that events similar to those (various allies being granted control of certain regions in Germany) happened throughout the period. It's fair to model these as vassals, I suppose.
As far as the events above go... I think several revolters (at least four) should become active in 1175, and they should all have "crown of Germany" events as well. The empire should take some big centralization hits in 1025, 1175, and 1122, and should get more centralized in 1158.