How could one develop a world in which the Vikings/Norse, Polynesians, and Mongols control the maximum possible territory and survive as global superpowers into the 1900s, all without straying into ASB territory? Maybe Polynesian and Norse conquests in the Americas and Australia, while the Mongols expand down into Africa?
Challenging but doable.
Polynesians: No pause in their expansion so they reach South America early and by early AD times have a solid, yet slow trade route (plus have colonised Galapagos and the Juan Fernandez Islands). Aotearoa is settled around that time. Maize, quinoa, and potatoes are dispersed throughout the area. With rapid growth all over Aotearoa they end up settling Australia and Tasmania. By the early 2nd millennia the Aotearoans unite although Australia is divided into numerous alt-Maori states. Each begins more extensive trade with SE Asia and China in this time, and a unified religion based on Buddhism, Hinduism, and Austronesian traditional beliefs emerges. Contact with Europe results in this religion solidifying, as well as the state deriving a more militant outlook after botched Spanish efforts to interfere in the region. In the 17th-18th century, a string of successful leaders conquers much of eastern Australia and during the 19th century, "Pan-Pacific" ideologies become popular which results in the remaining Australian states being conquered as well as colonisation of much of the Pacific. After victory in the Great War alongside Vinland over Japan and their European allies for control of the Pacific, the Aotearoans struggle against decolonisation ideologies which results in the formation of a federation of states named the Polynesian Federation. Nearly the entirety of Polynesia is under their rule. The modern Polynesian Federation has around 100 million people and a GDP of over 4.3 trillion [or whatever this world's equivalent of US dollars is]. They are a key exporter of resources and have a military capable of global deployment. Polynesia also is a leader in research in the fields of desert engineering, ocean sciences, polar research, and space research.
Mongols: The Mongol Empire conquers as OTL, with a notable divergence at Ain Jalut where the Mongols beat the Mamluks which is followed up by an invasion and conquest of Egypt. However, the Mongol Empire is similarly divided like OTL. But unlike OTL, the Mongols remain strong and powerful. In China, the Yuan are overthrown although the Northern Yuan retains considerable strength and returns in force following the collapse of the Ming, re-establishing the Yuan. In Russia, the Golden Horde reforms and retains considerable power. It converts to Orthodoxy and absorbs the Russian states and colonises Siberia while threatening Europe repeatedly over the centuries. It continues to reform to match Europe and emerges as perhaps the strongest country in Europe, challenged only at sea by the British Empire and on land by the 19th century Greater German Empire. After the Great War, it's dominance is secured as the most powerful country in Europe, a key exporter of nearly every resource, and the world's second largest food producer (after Vinland). It has a population of 725 million and a GDP of 25 trillion. The Golden Horde periodically intervenes in the Middle East to keep the Ilkhanate propped up, although the Ilkhanate's fortunes periodically wax and wane depending on its leadership. Still, it retains control of much of the Iranian plateau and nearby areas although by the 20th century, although it's little but a puppet of the Golden Horde, or "Tartary" as its most often called. However, skillful investment of oil wealth allows for industrialisation and the creation of a strong economy and its emergence as a strong regional power. They have a population of 105 million and a GDP of 3.5 trillion. The Yuan dynasty stumbles while modernising, allowing Japan to temporarily gain some strength and even defeat them in a war, but still manages to be a considerable power in the early 20th century. After the Great War in which they play a key effort in smashing Japan, their economy rapidly develops and they become a hyperpower. They have a population of 1.4 billion and a GDP of 40 trillion, the highest in the world in both metrics. In the modern age, the three states of the former Mongol Empire--the Iranian Khaganate, the Chinese Empire of the Yuan Dynasty, and the Tatar Khaganate--enjoy good relations despite some past tensions and different religions and even common languages under a shared ideology of "Borjiginism". These three states and many former parts of the Mongol Empire in the Middle East and Southeast Asia are organised into the "Asian Federation" which includes some shared economic policies and mutual assistance, which is sometimes nicknamed the "Neo-Mongol Empire" as the ceremonial president is elected from amongst Borjigin descendents. While Tatar, Chinese, and Persian are the main languages in each of the three countries respectively, a popular revival of Mongol (an archaic form of the Mongol languages spoken in North Asia) is used as an auxiliary language (including at the Asian Federation) and is spoken by many in these three nations and beyond. Further, the Tatar language and many Turkic, Tungusic, and so-called "Paleo-Siberian" languages have been written in a modified Mongol alphabet since the 16th century to promote literacy and national unity.
Norse: Unified Scandinavia (the United Kingdoms of Scandinavia) in the 15th century makes an early effort to recolonise Vinland. Over the centuries, Scandinavian settlers take huge amounts of land in the New World and Caribbean. In Europe, they conquer the Baltic, although lose much of it in wars with the Golden Horde or German states, while in the Americas, they expel the British and French from their holdings in the New World outside of some Caribbean islands and those south of the Chesepeake. In the late 18th century, they revolt over high taxes to support Scandinavian wars in Europe, but the rebellion is put down thanks to infighting amongst the rebels and becomes the focus of reform in the United Kingdoms of Scandinavia. By the early 19th century, pan-Nordicism dominates and creates the Atlantic Commonwealth, a union of all the Norse colonies in the New World stretching from the High Arctic to some smaller Caribbean islands (excluding the Southeast, thoroughly British). The Scandinavian king is offered the crown of Vinland by the Vinlandic colonies, which federates them and creates the Vinlandic Empire. Soon, Vinland takes the lead economically and colonises much of the west, and after the 19th century Western War, partitioning it with the Confederate States of America and Mexico at the Mississippi, Red River of the South, and 35th parallel north (with some altered borders in California based on topography). The Commonwealth's main rivals, Britain and Germany (ruled by communist states), start the Great War over various issues allied with Japan, Italy, and a few minor states, but the vast resources of Vinland and the Commonwealth's main allies, Polynesia, the Golden Horde, and China, allow their solid victory in the war. In the peace treaty, the Commonwealth restores the British monarchy but instead of restoring the unpopular former royal family restores a branch of their own royal family which had been deposed in centuries earlier. Bankrupt and without an empire, they join as an affiliate of the Atlantic Commonwealth. The modern Atlantic Commonwealth with its solid Norse heritage is one of the world's great powers. It consists of core members like the Scandinavian kingdoms and grand duchies (including Finland and Iceland), the Vinlandic Union, a union of colonies under the Emperor of Vinland, Scandinavia, and the North, and a few smaller African colonies and city-states around the world which share a common ruler, defense, and economic policy, and affiliate members who participate in some shared institutions. The core Atlantic Commonwealth has a population of 450 million and a GDP of over 30 trillion. It is perhaps the most prosperous state in the world and has global influence in numerous sectors.
Okay, I couldn't make Polynesia a true superpower compared to the behemoths of TTL, but they're far more powerful than that area OTL and an entirely indigenous polity. The former parts of the Mongol Empire (basically modern Russian Empire minus Poland, Alaska, and Finland/Karelia, Qajar Iran at their height, and Yuan China with Qing at their height's borders) are all superpowers, as is the Atlantic Commonwealth (most of the US/Canada plus Scandinavia, some Caribbean islands, and some Hong Kong-esque enclaves around the world).
