Jakandor is a setting for Advanced Dungeons & Dragons 2nd edition, released as part of its "Odyssey" lineup alongside such other 1e and basic updated settings like Savage Coast (a 2e update of Red Steel).
Known as both the Island of War and the Island of Destiny, Jakandor takes place on a single massive island, divided between two warring factions of humans.
On the eastern half, you have the Knorr, an Iron Age culture of warriors and hunters, settlers from a distant land who venerate the concept of vengeance as essential to keeping the spiritual balance of the world in check. In their homeland, the Knorrmen were as they are today; simple hunter-gatherers who found themselves unexpectedly enriched when foreign traders stumbled upon their lands and chose to trade with them. Eventually, this led to sharp cultural divisions between those who wished to embrace the foreigners and their culture and those who wished to maintain the old ways, in particular the rights of raiding and honorable warfare. Not helping was that these foreigners, who had once been honestly named as Allies, eventually began to see themselves as masters over the Knorr and not their equals, demanding that the Knorrmen begin to abide by their laws and punishing them for refusing. A Knorrman priest of Kenn Durem, one Solkon Dred Kolra, found his clan's magic failing: blaming this on the spiritual corruption of the Allies, he animated a massive golem and used to to level the harbor where the Allies gathered. In revenge, the Allies hired mercenaries and sent them into battle to punish the Knorr, who also fell into infighting as a civil war ripped clans and families apart over whether to side with the traditionalists or the Allies.
This all came to a head in a pitched naval battle between the traditionalists and the Allies, one that the priests of the Knorrmen swore was herald to an apocalyptic cleansing of the world by their goddess, the War Mother. During the battle, a huge storm erupted that swept the fleet of Knorrmen far westward into the sea. Naturally, they viewed this in a religious light, believing that the War Mother has destroyed their homeland for abandoning her and that it was now their sacred duty to sail westward and found a new homeland. And, after traveling westward for weeks, they came ashore at Jakandor. There, they came to the City of Eternal Light, home to the Broken People - the last remnants of the old world's evil. Now, the Knorrmen battle to cleanse Jakandor of these foul wizards and their necromantic minions, in order to prove themselves worthy enough that the War Mother will restore the old world. Although this remains their overarching goal, the traditions of their people cannot be denied, and so there is endless war of Knorrman against Knorrman as well as against the Broken People.
Of course, the truth is... not quite so much as the Knorr's sagas tell it.
The "Broken People" are the Charonti, a culture of wizard-priests who called Jakandor their home long before the Knorr fell upon their shores. To the Charonti, duty and justice are what makes a person human, fueled by a deep religious devotion to their creator, the God of Life and Death. Driven to advance knowledge and understanding, they consider necromancy to be not a blasphemy, as in some cultures, but the epitome of their creator's blessings. Through this magic, the ancestors can return to walk at the sides of their descendants, serving the community even after life has fled by offering strong, unyielding efforts at manual labor, freeing up the living to focus on learning and thinking.
Thousands of years ago, the Charonti held a mighty empire that stretched well beyond Jakandor, but a terrible sickness known as the Wasting Plague that fed on magic to sustain itself devastated their lands. Only now, over five thousand years after their empire fell, are the Charonti truly trying to rebuild. That is not made easy by the presence of the Knorrmen, who ever since their arrival over 150 years ago have dedicated themselves to destroying the sacred undead of the Charonti, killing those Charonti who still live, and pillaging and/or destroying the remnants of Charonti culture.
Long story short? Barbarians made by blending Vikings and Native Americans (with a dash of Celts) invade the island of a post-apocalyptic magocracy of Aztec-Japanese necromancers and declare a holy war on the natives, who're equally determined to wipe out the foreign invaders. Bloodbaths ensue.
Jakandor is fairly unique for even Odyssey's "mini-settings" in that it was made of three books; Island of War (the Player's Handbook for the Knorr), Isle of Destiny (the Player's Handbook for the Charonti), and Land of Legend (the Dungeon Master's Guide).
Incidentally, Jakandor sells itself on its murky morality, depicting the conflict as one with no clear "good guys". That's a little hard to swallow when all three books pretty bluntly admit that the Knorrmen are ever-fractious warlike foreign invaders.