The Crusade is the name Feldia gives to the sequence of campaigns, several centuries ago, in which a combined religious force out of Kretavia crossed the Sea of Coin and made war on the pagan north until the north converted. It is the hinge of Feldian history. Everything institutional in the country — the Church, the vocabulary people argue theology in, the calendar most duchies keep — postdates it, and everything older than it survives underneath rather than alongside.
Dates are not agreed. Feldian chroniclers place the first landings anywhere across a span of decades, and the Kretavic reckoning uses a different calendar again, so that the two accounts cannot be laid side by side without an argument about arithmetic first.
Before
Pre-Crusade Feldia was pagan, though the word flattens what it describes. There was no church, no doctrine and no priesthood in any sense a modern Feldian would recognize. What there was instead was practice: river spirits, forest presences, rites tied to harvest and flood and the turning of the year. The land was held to have opinions and people answered them. Whether that constituted a religion is a question Feldian scholars have been enjoying for a long time, largely because answering it has no consequences.
The invasion
The campaigns came north, which is worth stating plainly because it is the fact Feldians most often forget and Kretavians never do. Desert armies crossed the water to convert farmers, not the reverse. The force was religious in organisation as well as motive — a coalition of southern traditions already unified under a shared theological framework, arriving with clergy, scholars and a supply train, which suggests they intended to stay long enough to teach.
Militarily the Crusade succeeded. Culturally it succeeded further and lasted longer. When the campaigning ended and the armies went home, what remained was not an occupation but a religion: the single creator God, an institutional structure to administer belief, and the theological vocabulary Feldia still argues in. The Feldian account of this period is not a comfortable one and tends to be written in the passive voice.
The division
What Feldia teaches next is the point on which the two countries part.
The Church in Feldia holds that some years after the southern faith had taken root, a figure appeared in Feldia — that he taught, that what he taught completed rather than contradicted the revelation the Kretavians had brought, and that the faith as Feldia now practices it is the whole of a thing the south had only in part. This is the settled teaching of the Feldian Church and the ordinary belief of the country. It is not a matter on which Feldian bishops disagree, which distinguishes it from almost everything else they discuss.
What can be said without contention is that the Feldian faith changed at this point and the Kretavic faith did not. Kretavia declined the addition. It has never accepted it, and it holds the Feldian position to be a corruption of an older and correct revelation — a fabrication in the Kretavic telling, at best an error sincerely made. The Kretavic account, in short, is that the work of the Crusade was interrupted before it was finished, and by the very people it was performed on. Feldian and Kretavic writers have been unable to discuss the matter for three centuries without it becoming a discussion about something else.
The faith that resulted
The Feldian Church is syncretic by origin and shows it. It absorbed a conquering religion and then absorbed a further development on top of that, and it has never possessed a fixed canon, because it was never built from a single source. It grew. Different duchies took up different emphases at different moments; the text kept at Kirchberg and the text kept at Kronstadt diverged early and have not been reconciled, and no one with the authority to reconcile them has thought it worth the fight.
The older practice was never removed either. It was layered over. In Waldheim the layer is thin enough that the Church has stopped making a point of the matter; in Kirchberg it is thick, and documented, and studied by people who would be offended to be told they still keep any of it. It is present everywhere in between. See Folk Belief and the Uncanny.
Why it still matters
Kretavic missionaries travel in Feldia and travel armed. From the Kretavic perspective this is neither aggression nor discourtesy but resumption — the work was never completed, and it remains the highest calling their faith recognizes. That is a considerably more difficult thing to negotiate with than hostility would be, and Feldian port authorities have never found a policy that satisfies anyone.
The raiding on the Seehaven coast is understood in that duchy as the same project by other means, and no argument about the distinction has ever survived contact with a burned village. The unexplained warmth between Eisenmark and Kretavic merchants is read in the same light by anyone inclined to read it at all.
Jrakvia missed the whole of it. Three centuries of uninterrupted development happened there while Feldia bled through invasion, conversion and schism. The Jrakvians watched from across the water, drew their conclusion about what religious war produces, and shut the door. Feldian writers who find their isolation baffling tend not to have read this article first.