I reckon international relations would be less tense. I may just be over optimistic, but I think each bloc would be happy with what they have, and so problems could be solved by the group of empires as a whole.
I agree. Morevoer, I have yet another "imperial" scenario, a backburner TL scenario of mine.
- PoD is the survival of Frederick I Barbarossa to complete the Third Crusade and of his son Henry VI Hohenstaufen to a successful long reign respectively. This creates a strong basis for the gradual centralization of the HRE, and enables its transformation into a hereditary monarchy at the very end of the 12nd century. Their talented scion Frederick II is educated to complete the basic job of empire-building, which he does over his own decades-long equally-successful reign. Some intermittent civil wars in Germany and Italy see the resistance of particularist nobles and city-states crushed and gradually snuffed out. Another long reign by his son Conrad IV, in a dynasty notable for the longevity of its talented rulers, sees the Western Roman/Carolingian Empire definitely being reborn in the eyes of its subjects as the most powerful centralized European monarchy spanning Germany, Italy, Austria, Bohemia-Moravia, the Low Countries, Burgundy, Switzerland, Slovenia, and Dalmatia, its armies swelled by the manpower of Germany and Italy and its coffers filled by the taxation flowing from the trade centers of Flanders, northern Germany, Franconia and Palatinate, Bohemia, northern Italy, and Sicily.
- The power struggle between a stronger HRE and the theocratic Popes leads to an early Great Schism, which eventually ends in the defeat and marginalization of the Papacy and the Curia. The Western monarchies eventually turn to propping up the power of the national episcopates and keeping a tight leash over them, in order to affirm secular control over their respective national clergy. Latin Church becomes quite decentralized, with the clergy of each nation being governed by the local episcopates, subordinate to the secular governments. The Ecumenic Council once again becomes the only authoritative body for the whole Church. This allows the reconciliation between the Latin and Greek Churches, and the end of the Eastern Schism. The Reform as we know it never happens, although the Western Church as a whole evolves to resemble the Episcopal in structure.
- The national unification of France is wrecked, and the fortunes of its neighbor states boosted, when the HRE interferes in the struggles between the Kings of France and the Angevin Empire on one side, and Aragon, France, and the Counts of Tolouse, on the other side. This results in the Plantagenet dynasty successfully keeping and eventually uniting England and their feudal possessions and conquests in northern and western France into a centralized state. The Angevin Empire is also able to affirm its supremacy over Ireland and a Scotland.
- Aragon, not the Capetingian French monarchy, annexes Languedoc and Provence during the confused mess that the suppression of the Cathar heresy becomes when mixed with the Great Schism and later during the War of French Succession. Aragon is able to capitalize this added power into gradually uniting the other Iberian Christian states under its control during the successful Reconquista and the WFS, and to seize Corsica and Sardinia, forming the Iberian Empire. Sicily and southern Italy, however, remain wholly outside its grasp, due to the overwhelming grip of the HRE on Italy.
- The kingdom of France is stalemated in its expansion down to an unhappy, landlocked buffer state (and occasional recurrent battlefield) between the growing imperial behemoths of the HRE, the Angevins, and Iberia. In the 14th century, it suffers a dynastic crisis, and the War of French Succession happens, which sees the decisive victory of the HRE, the Angevin Empire, and Aragon over France, Castille, and Scotland. France is eventually partitioned between the Angevins and the HRE. Iberia swaps its share with Britain in exchange for southern Aquitaine.
- The kingdoms of Denmark, Norway, and Sweden are pushed into forming a lasting Kalmar Union for mutual protection from their powerful neighbors.
- The strength of the HRE makes its expansion in Eastern Europe highly successful: Poland and Hungary are gradually turned into vassal states, annexed, and assimilated by the HRE.
- The ATL equivalent of the *Fourth Crusade leads to a dynastic change and reform in the Byzantine Empire which is much less destructive (no Sack of Costantinople) than OTL, an alliance with the HRE, and the eventual revitalization of the Byzantine Empire. The ERE gradually recovers full control of Anatolia, Greece, Macedonia, and is later able to conquer the Levant, Armenia, and Mesopotamia. Serbia, Bulgaria, and Wallachia-Moldavia become vassal states of the ERE and are gradually annexed and assimilated.
- The strength of Britain, Iberia, and the HRE leads to a successful new round of Crusades and the expansion of the Reconquista in the 15th century. As a result, Iberia conquers North Africa. The HRE seizes Eygpt and Nubia and turns them into a vassal state, later expanding it into Ethiopia. The HRE-ERE alliance eventually conquers Arabia and Persia (the HRE seizes Hejaz and Yemen, the Byzantine Empire the rest). Those areas are gradually and forcibly Christianized. This is paralleled by an Hindu revival in India and Indonesia, which over the centuries leads to the marginalization and destruction of Islam as a major world religion.
- Mongol invasion of Europe does not really reach any further than Poland and Hungary, and the Tartar onslaught mostly ravages the Middle East for a while, further weakening Islamic states against the Crusader-Byzantine assault. After the Mongol Empire breaks apart, support by the HRE and the ERE allows Muscowy to swiftly oust the Golden Horde and build an empire in European Russia, which later expands to northern Caucasus, western Siberia, and most of Kazakhstan. By a parallel process, a Christianized Prussian tribe (TTL Lithuania equivalent) is able to expand and create a state spanning the Baltic lands, White Russia, Ukraine, and the former Khanate of Crimea, which later gets absorbed by Russia.
- Colonial European expansion leads to the Americas and later South East Asia and Oceania later still subsaharian Africa being carved up by HRE, the Angevins, Iberia, Scandinavia, and ERE, while Russia colonizes Siberia. China and India suffer colonial penetration fro a while, but eventually they are able to modernize to become imperial great powers on the same standing as the European ones, which in modern times leads to India absorbing Baluchistan and Burma, and China absorbing Korea, Japan, and mainland South East Asia.
- Over time, the European powers are strong enough to suppress separatist revolts in their colonial empires, and far-sighted enough to grant fair economic terms and an amount of confederal autonomy to their American and Oceanian colonies and later to the African and Asian ones, which leaves them linked to Europe.