*Shrug* 'National' differences are nowhere that important in this period (and there are very very good chances that the modern rise of European nationalism is butterflied out or it takes a wholly different, much less ethnic-linguistic, character, if Central Europe is dominated by a supranational empire that is the most powerful European state since the High Middle Ages). Peasant dialects got substantially different within a few days of horseride travel anyway, and Latin was the widespread lingua franca of religion and culture for the educated European elites. A successful HRE may easily embrace and foster its use as the imperial lingua franca for administration and trade. The HRE is surely going to paint itself to its own peoples and to Europe at large as the Second Coming of Augustus and Charles the Great, with neo-Roman imperial ideals being used to smooth out petty "national" differences between the various peoples. Germans and Italians are going to be close enough to balance inthe foreseeble future (especially because this divergence is necessarily going to butterfly out the 17th-18th century hard decline of Germany and Italy) within the Empire, as it concerns demographic and economic weight, that the supra-national imperial ideal may easily look believable to both. Slavs of course are in a quite different position, but then again they have a snowball's chance in Hell of resisting assimilation in this scenario. As it concerns Romance-speaking 'Burgundians', in all likelihood they eventually merge with Italians.
Two comments - well, three.
1) Scotland still has a sense of itself as separate from England even OTL (in this period). It isn't about being Celtic in the sense of "we're Celts and you're Anglo-Saxons" as a people, its a different legal and cultural set of traditions entirely. That kind of "nationalism" is not going away because the educated elite and the clergy speak Latin (and Latin as a lingua franca seems...easier said than done.)
2) Neo-Romanism is going to mean exactly what? The HRE can paint itself as the survival of/reincarnation of Charlemagne's Empire until its forgotten the differences and it still has to be something people take seriously. Not to mention something that isn't just a fancy term for whatever fantasyland the Staufen dream up, like the Moon King's castles were.
3) See the bottom of this post for comments that relate to Poland.
Well, Frederick II already got to be 56 y.o. IOTL, and if anything, the scenario doing just as well or being slightly more longeve, with a less troublesome reign. The PoD just really requires Henry VI and Conrad IV doing 50 y.o. or better, with Conrad V being allowed to croak at 40 or so, which is far from implausible.
For comparison, treating Philip as equivalent to Henry VI (they were born in the same year).
Philip II: 58
Louis VIII: 39
Louis IX: 56 (only 10 when his father died)
Philip III: 40
Average age at death: 48.
So 50 is actually not entirely unreasonable by comparison to a dynasty in roughly similar circumstances.
It is, however, interesting how both Louis VIII and Philip III die "young", the former leaving a minor as an heir. To continue this, Philip IV died at 46. That would make the average age a little under 48 instead of a little over.
Rounding to the nearest year for kingly death for purposes of the calculations on averages.
So while this scenario takes it for granted that the Staufen do not have a succession crisis through out the 13th century, for the sake of discussion (as this is on the specifics not covered by the well trodden path of these scenarios), it ought to be noted that the bumpiness of this - while not cutting them off as OTL - can have some unpleasant consequences for unexpected reasons for Frederick II and his son and grandson.
Henry VI's relative longevity also being in the taken for granted assumptions.
It ought to be noted that in the Prince of Peace, Frederick dies at 48 (if I am not mistaken) and is not succeeded by his son. Just for completeness's sake.
Agreed, but the Duke of Bavaria should not be any different from the Count of Champagne in this regard.
That's quite thorny enough, though. Not "this is impossible", but certainly "this is a challenge".
Uhm. I do expect something of an economic boom within the HRE as basic centralization progresses to fulfillment over the late 13th century, up to the plague. The effect of integrating so many prime economic centers of Europe within the same united polity, imperfect as a late middle ages unification may be, is going to be substantial. And this is going to have some significant effect on population (not to mention the state's coffers).
As an aside, this in all likelihood accelerates the Renaissance significantly (more so if it delays or forestalls the fall of Outremer), but of course not radically, out of greater opportunities for mecenatism, increased trade exchanges, and the like.
How exactly though? How is a greater level of "national" unity going to make one bit of difference to the trade routes within the state compared to OTL?
Certainly in later eras it'll be a huge difference, but how much real difference does it make whether Milan differs to Nuremburg vs. ignores it as much as it can when it comes to trade and agricultural production?
IIRC, the Poles have somewhat better land than the Prussians. And Poland is not very likely to pull itself back together. The Emperors and the eastern magnates had any interest to keep it fragmented, as a preliminary to its assimilation.
It is also somewhat harder to take over.
Anyway, in the end a strong, united HRE is going to expand in Poland AND the Baltic over time, with the locals having much less of a chance than OTL to forestall its expansion. We may disagree on which area would get priority in various periods.
A strong, united HRE is going to expand to the east so much why again? Again, if its thinking of itself as Carolingian, its going to want to reincorporate - in some sense - France. More at bottom again.
Note: This is discussing generalities as far as possible (same applies to the rest of this post). It would not be inappropriate for any given scenario to be more Eastern-centric or not, but there's a difference between how any given HRE Centralizes scenario may devour Poland and the Baltic and what applies as a generalized reality as part of the basic factors at play, the way that for instance all scenarios must address the Pope in some form.
Anytime up to the 19th century, when settlers keep expanding in an area from a neighbor polity, and that polity is stronger than the nominal owners or rival claimants of the area, there comes a point when settlement becomes ownership by one way or another, ask Mexico.
This is not a matter of "nominal" ownership, even if the Polish states are weak as polities, they do control their own territories - and those territories are already reasonably well inhabited.
So this is not at all like Mexico's situation relative to the Americans.
I'm not saying that ITTL whole Poland gets Germanized up to the Vistula and part of the HRE up to the Bug, this may or may not happen although it is far from outlandish. But if at the very very least West Prussia and South Prussia (the Prussian share of the 1st and 2nd Partitions) do not end up as German as pre-WWII Silesia ITTL, I'm going to cry there is a quite unreasonable amount of Polonophile bias in the TL. If an identifiable Poland survives at all ITTL, it really needs to be pushed rather more eastward and southward than OTL (in pre-WWII terms of course), with Warsaw being a border city or nearly so, like Krakow, and essentially made up of Masovia, and Sandomierz, and maybe a shurken.
How is there an unreasonable amount of Polonophile bias for the HRE to not carve up Poland? Poland is not vital to the HRE in any way, or part of its historical claims in any sense - at least not to the extent being proposed.
Could the Staufen mess with Poland if they so chose? Definitely. That is an obstacle that needs to be weighed, but it is not a situation where Poland being broken is a big part of the nature of such a timeline as is being sketched out in general terms.
It is not necessairly going to do better, but it would be wholly reasonable for it to do so by indirect butterflies. I do really expect the success of the Staufen to cause at least one more successful Crusade, quite possibly two, or even three on a stretch (not necessarily or even likely all of them at the Staufen's hands), and the Fourth Crusade in all likelihood to have a wholly different course. I'm just calling everyone's attention to the possibility of it happening, when we discuss things like the Teutonic Order.
Possibility, yes. Probability...gets into a lot of factors that aren't even addressed by the Staufen succeeding in Germany and Italy.
Well, Nuremberg indeed has very good chances to end up as the capital of the HRE by default if political inertia about the issue prevails, especially because it was part of the Staufen demesne, and its position is not admittedly so bad as it concerns the geopolitical balance between Germany and Italy. Munich may only have chances if the Emperors at some point get a bug for purposefully creating a 'new' capital with near-optimal geographic placement (as much as the Alps would allow, anyway).
Once the centralization process gets so advanced that an itinerant court, 'viceroyalty' sub-capitals, and such, become much less useful, I do expect the Emperors to turn and get rather lavish with creating a quite striking imperial capital. This would fit with the neo-Roman imperial ideology, and work as a magnet to drag the nobles and magnates close to the imperial throne.
I'm not sure how much neo-Romanism is going to mean, but this is mentioned above and relates to that in general rather than specifics on if it happens how it will influence the capital.
For the sake of being concise, I think we need to address the issue of Poland as primarily these two things: rather than the three or four specific little bits of quoted text:
1) To what extent is Poland relevant to the goals and objectives of the Carolinginan Empire Reborn? Certainly such an empire can meddle. But would it choose to spend the effort in all ways to do so, or would it pursue other things? How much will the Staufen
care to have more than a nominal overlordship of Poland? How much will it be possible for magnates to tear away pieces?
2) To what extent will there be - in this period (keeping in mind that at the end of the 13th century Poland is pretty close to reuniting, OTL - its a generation off if memory serves) a greater German presence in Poland that leads to Polish lands being drawn into the HRE as opposed to Germans settling in a foreign land?
Obviously one can easily construct something where the Staufen and other Germans find Poland irresistible, that is not in dispute. But Poland can also be a side project, and as such is more likely to resemble OTL fairly closely, than to be assimilated.