The plane of Alara was once a single, immense, plane, rich in mana and natural resources. Unfortunately, we can only imagine that world now; Alara as such is no more. Many centuries ago, Alara was stripped of its mana in a cataclysmic planar event, perhaps brought on by the actions of a long-lost planeswalker. The drain on Alara's mana shattered something deep in its metaphysical structure, causing it to undergo a radical planar refraction. The plane broke into shards along mana lines, diffusing into its component parts like light refracted into a prism, and shattering Alara's civilizations and ecologies along with it. Whatever agent caused this destruction abandoned what remained of the plane, its spell presumably finished.
The shards that resulted from Alara's refraction drifted away from each other in the Blind Eternities. They were planes unto themselves, but not complete. Each was cut off from two different colors of mana. The plane that became Bant, for example, lost its connection with black and red mana. The plane of Jund was severed from its blue and white, and so on.
As the shards' mana supplies slowly replenished themselves again, this mana imbalance dramatically altered life on each world. Environments warped to match the changed mana landscape, and life changed with it. Many species fell to extinction, while new forms of life adapted and prospered. On Esper, without wild green or red magic, nature fell by the wayside, while all-controlling wizards rose to ascendancy. Grixis, lacking the life magic of green and white, became a realm of undeath and necromancy. In this way, each shard evolved to become its own unique world.
Main article: Bant
Rules by the hierarchy of angels that fill its crystal blue heavens, Bant is a natural and cultural utopia. Castle spires rise majestically over golden fields. The sun reflects in the polished armor of rows of knights. A rigid caste systems determines the role of every member of society, yet corruption is nowhere to be found. Bant is a place where true community has found a home.
Main article: Esper
Esper is a world where powerful magic has trumped nature. Human and vedalken mages control almost every aspect of life here, from the tides and winds to the shortcomings of the flesh. An agency called the Ethersworn has made it their mission to infuse a magical alloy called etherium into every living creature on the plane, following the doctrine of the plane's enigmatic sphinxes.
Main article: Grixis
Grixis is no place for novice travelers. Swarms of undead, rampant death magic, and demonic influence make Grixis an abominable destination best avoided by most. However, Grixis is home to some of the shrewdest forms of necromancy practiced anywhere in the Multiverse. If you seek knowledge of the necromantic practices, it can be a worthy place to study.
Main article: Jund
Jund is a plane-spanning web of predation crowned by dragons. Nature is in its rawest, most treacherous stage here, devouring all not prepared for its dangers. Whether you face Jund's human warrior tribes, its packs of viashino hunters, its might dragons, or simply its carnivorous flora, your survival skills will be tested to their fullest. It's saying something that feisty goblins, who cling desperately to the bottom of Jund's food chain, are the safest foes you'll face.
Main article: Naya
As a trropical jungle-place people with perfect specimens of the human, elvish, and leonin races, Naya seems like a paradise. But don't let its exuberant cultures fool you; Naya tremors with peril. Behemoths taller than buildings lumber through Naya's rainforests, crushing acres of vegetation, or civilization, casually underfoot. Yet somehow, Naya's sentient races revere these gargantuans, relegating them to the pinnacle of their religious beliefs and ascribing them a sacred ineffability. Travelers wil surely experience culture shock of the tallest order among Naya's vine-dense glades.