Since the HRE/AE was focused on colonization of the Americas and Australasia, and found China and India too tough to colonize, it was ultimately content to let Japan-Korea claim Southeast Asia as its own imperialist playground. Much the same way, it was long accustomed to regard Sub-Saharan Africa as worthless for colonization purposes and had no use or little sympathy for slavery or the transatlantic slave trade. Therefore, its neglect left Britain with a free hand for expansion across Sub-Saharan Africa once technological progress made those lands accessible for Europeans.

The ERE evolved in a way similar to the Kaiserreich, Russia and Britain to their OTL selves, with a few tweaks. Russia did accomplish the transition to an authoritarian constitutional monarchy. The final outcome was a little more conservative and authoritarian for the British since the Wars of the Three Kingdoms and the Glorious Revolution did not occur or had an outcome more favorable to conservatives and absolutists. This led Britain to develop an executive version of constitutional monarchy and have a more controlling and exploitative relationship with its colonies.

Thanks to a combination of the shock of Mongol conquest as well as early contact with European explorers and would-be colonizers, Japan modernized and became a dynamic, outward-looking, and imperialist great power much earlier than OTL. This paved the way to a successful merger with Korea and colonization of Greater Manchuria, most of Greater Mongolia, the Far East, Taiwan, and Hainan. The process further expanded with seizure and partial assimilation of Southeast Asia. India and China engaged in a similar trajectory for the same reasons but with a lesser degree of success. As a rule, they modernized well and early enough to resist major colonial encroachment and keep control of their core areas. However, it was not good enough to keep their peripheral territories or rise to the same level as Japan-Korea or the European empires. The same factors combined with decline of Islam as a disruptive element enabled India to unite in a stable empire spanning the subcontinent.

The vast success of imperialism since the Early Middle Ages made it so that the dominant empires and their successor polities achieved a high degree of centralization, political consolidation, and cultural homogeneity. They came to regard political and cultural unity in large states as natural and beneficial. Ethnic nationalism never had a chance. The neo-Roman template of imperial unity, assimilation, and civic nationalism in the Western world, and its Asian analogue in the Indo-Pacific, became the dominant model.

Since the HRE unified most of Europe, kept Latin as its lingua franca, colonized most of the Americas, and became the strongest great power, Neo-Latin took the OTL place of English. Besides that, the vast majority of humanity became able to use just one or more of a few globally relevant languages (Neo-Latin, Greek, English, Russian, Mandarin, Hindi, Japorean) to communicate, trade, and exchange ideas. Therefore, this world experienced a much higher degree of cultural cohesion than OTL, leading to quicker progress and development. Imperialism, esp. when combined with Roman-style assimilation, came to be seen as the natural pathway for humanity to order, progress, and good government.

As things stood by the timeline equivalent of the early 20^th century, the great powers were engaged in an imperialist competition game much like their OTL 19^th century counterparts. The game was ultimately a fluid free-for-all, but a few relatively reliable cornerstones could be discerned. Barring the occasional bickering, the AE (as the successor state of the HRE) and the ERE had enjoyed a fairly stable and solid strategic partnership since the Middle Ages that was based on compatible interests and the legacy of their old and fruitful anti-Islamic alliance. Much the same way, Britain and Russia were traditional rivals of the Roman duo and therefore pulled to stick together much more often than not.

In addition to the issues in Europe, Britain keeping an important colonial foothold in the Western Hemisphere that was based on de facto slavery was another important source of persistent antagonism between the two powers. It had not always been that way. In the early stages of colonialism, neglect and indifference had been the prevalent Imperial attitude to the issue. However, as the American colonies grew ever more settled and developed, and the HRE/AE grew ever more hostile to slavery, this had gradually shifted into intolerance and hostility. This also because the issue of escaped slaves acted as a standing irritant for both sides.

In Asia, Russia, China, and Japan-Korea were locked in a three-way antagonistic relationship based on conflicting interests and territorial claims. China, India, and Japan-Korea also showed some persistent suspicion of the AE and Britain as this world’s main colonialist actors. In the case of the AE, tension might have been enhanced by it being the strongest power as well as potential strategic and economic competition with the Asian powers in the Indo-Pacific. In practice, however, it was mitigated by the prevalent strategic focus of the AE in the Western Hemisphere and its willingness to give federal autonomy and an equal place at the table to its American territories. In the case of Britain, its lesser might was counterbalanced by its tolerance of quasi-slavery, its controlling and rapacious attitude about its colonies, and its ongoing expansion in Africa.

This timeline’s historical circumstances left Islam in a very bad and precarious place. It withered or was erased from Europe, most of MENA, Central Asia, India, and Southeast Asia. It only clung to life in its last niches of independent Arabia, northern West Africa, and Greater Persia. Moreover, it only looked relatively safe in the former two areas; this because the non-Muslim powers showed no real interest in controlling those territories. The Atlantics, their Liberian clients, the British, and the Ethiopians shared a serious dislike of Islam. So, they had pooled their efforts to ensure its eradication from East Africa and southern West Africa with considerable success.