Alara was whole once. But that was millennia ago. Where once there was a plane, now there are five: the Shards.
The plane of Alara was a world rich with mana, a world in balance...until the Sundering. In a cataclysm of unimaginable proportions, Alara was rent asunder into five separate worlds, each a refraction of the others.
The cause of this cataclysm has been lost to time. Some ancient lore of the Shards suggest a being of godlike power forcibly split Alara to seize its mana for himself. Some believe it was caused by the titanic battle for the fate of Alara, waged by the archangel Asha and the demon Malfegor. But for most, only the dimmest cultural memories remain of a richer world that existed before their own.
Whatever the cause of the splitting, one thing is clear: The Shards have become very different places in the time since the Sundering. Each plane was all but severed from two of the five colors of mana. The Shard of Bant, for example, lost almost all its black and red mana, maintaining only white, blue, and green.
This mana imbalance caused the Shards to evolve in wildly distinct directions over the course of thousands of years. Now only hints of a common ancestor plane remain on the five worlds, and their environments and denizens could hardly differ more.
Naya. Life, passion, community, and the wild—these are what flourish without the influence of black or blue mana. In this lush land, life is celebrated. Instinct triumphs over machination. Here titanic predators are shown respect, while humans, elves, and catfolk called leonin seek to revere and respect nature.
Bant. Without the destructive or selfish impulses of red and black mana, Bant has become a golden utopia. Angels rule the realm with benevolence and grace. Humans and the birdfolk called aven resolve their conflicts with ritualized combat. Duty and honor are the bedrock of this kingdom of light.
Esper. In this world of wind and wave, control is the guiding force. Cut off from the chaos of red and green mana, Esper has become a magocracy. Enigmatic sphinxes counsel powerful wizards and seers. Everything here is observed and controlled. The forces of high magic rule supreme.
Grixis. What becomes of a world without new life? The dark wasteland of Grixis answers the question. Its denizens desperately cling to its remaining lifeforce. Without the communal forces of white and green to bring life and compassion, it's every ghoul, demon, and necromancer for themselves.
Jund. In the absence of white or blue mana, Jund has devolved into a roiling, primordial cesspit. Dragons top the food chain, at home in Jund's countless volcanoes. While dragons stalk the skies, humans, goblins, and the lizardfolk called viashino lie low in Jund's tar-spotted, vine-choked canyons.