I've always been interested in the Crusader States. Most of what we've been taught about the Crusades in our middle school history classes is not true (although it would have been true for the Northern Crusades, actually—but not for the Middle Eastern Crusades that most people think of when they think of the Crusades.) It's not that the history of the Crusades is some secret; it's just that we're exposed to a narrative, and most people are relatively incurious, so they don't ever learn anything beyond the narrative.
The Crusades were a mercy mission (to use Darth Vader's term)—the advance of the Muslim savages had conquered vast swaths of Christendom, and many Christians were killed, enslaved, or otherwise oppressed. You can see the end result of this today where there are effectively hardly any Christians at all left in Anatolia, the Levant, or North Africa—all of which were part of Christianized Rome at one point.
The Byzantine Empire actually plead with the Pope for aid, and the First Crusade was called by Pope Urban in the year 1095. Although it probably wasn't what Greek Emperor Alexios I Komnenos really hoped for, although he did save and rejuvenate his Empire; a process known as the Komnenian Restoration—but because of the schism between the eastern and western churches which dated to 1054, the Crusaders did not turn their territory regained back to the Byzantines, but rather set up their own Crusader states, which lasted for several centuries before succession crises, civil war, and neglect from Western Europe set in and they gradually faded away to be captured again by the Mamluks.
In addition to the Kingdoms of Jerusalem or Cyprus, the Principalities of Antioch and Cilicia, or the Counties of Edessa and Tripoli, etc. there were Crusader states in the Balkans as the result of later Crusades—attempts to roll back the advances of the Ottomans over what had been the Byzantine Empire. And there were northern Baltic Crusader states, established up north where the last heathens in Europe still resisted assimilation into Christendom.
In part, they eventually failed due to simple greed. Had the original purpose of providing aid to struggling Christians and the recovery of their lands that had fallen to the paynim been maintained, it would have been one thing—but later Popes saw the Crusades as an opportunity to militarily repair the schism of the Eastern church by forcing them to rejoin the West. It was largely probably responsible for the eventual fall of the Byzantines, and possibly for the fact that the paynim were later able to roll up through the Balkans to threaten even Vienna itself before they were finally halted and pushed back—although not as far as they had been. The Northern Crusades didn't even have that flimsy of a justification—the Church wanted to impose Christianity at the end of a sword on the Lithuanians, Old Prussians, Livonians, and Estonians, etc.—plus give ambitious knights and rulers a chance to establish conquered fiefdoms in new lands.
For nearly 400 years the Crusades were an on again off-again proposition. At the same time a few other interesting things were happening in Europe. Although not a declared Crusade per se, the Iberian Christians had been rolling back the Muslim conquest there in the process called the Reconquista for almost 400 years in a similar manner; and this was finally completed officially in 1492—only five years after the end of the last official Crusade.
Also; Anglo-Saxon England was conquered by the Normans just a few years prior to the start of the First Crusade. It was almost conquered by the Vikings, who were really just starting their own Christianization at the time and although their kings had been Christians for a few generations, many of their people still were not. Harald Hardrada was, before being a claimant to the English throne, a claimant to the throne of Norway, he had spent considerable time in Kievan Rus (also only recently officially Christianized) and served as a Varangian captain in Constantinople. After the conquest of England by the Normans, many Anglo-Saxons fled the country and even served as Varangians to such a degree that in the time of Alexios I Komnenos it was perceived as an English unit.
After the Crusades and Reconquista were over, the rules of Europe could turn to other matters. Columbus set sail only five years after the last Crusade and literally the same year that the Reconquista ended. There's a fair bit of evidence to suggest that knowledge of Vinland and the Viking settlements and the idea that there were lands out there on the other side of the Atlantic wasn't exactly in as short supply as many would have you believe, and that Columbus may well have been familiar with exactly these tales. Now, no doubt he never suspected an entire hemisphere with two continents and tons of islands... but he already knew that the world was round, and he already knew that there was land out there within sailing distance. Most likely. Otherwise, he would never have made the attempt.
But what if... the Muslim conquest was never really as big a deal as all that to begin with? What if... instead of Crusades to liberate the Holy Land and relieve the suffering of Christians in what was once the Roman provinces of the Levant, north Africa, Anatolia and the Balkans were able to successfully fight off the Muslim conquest, and remained independent Christian kingdoms?
What if this led to earlier exploration of the New World? If Anglo-Saxons displaced by the Norman conquest fled West across the Atlantic instead of south to Constantinople? If Vikings settled more thoroughly there following in the wake of the Anglo-Saxons? If Crusader States were established in the New World by around 1100 AD?
And what if they were then cut off and were unable to return to the Old World, and those in the Old World were unable to reach the New World in turn? After a generation or two, what would these Crusader states look like? And what if it wasn't the actual New World, but a fantasy analog of it?
And that... is what DARK•HERITAGE Mk. V is.
I should probably stop talking about it at the High Concept level and start getting some details going. Maybe next time.