Five worlds have merged into one. But the Conflux is no gentle reunion. There's no delicate re-weaving of planar boundaries. No amicable fusing of cultures. No teary-eyed reconciliation of old friends, no back slapping or "you haven't aged a day." These are worlds that have been invaded by alien lands, by cultures and creatures they've never dreamed of before. The lands of the shards overlap, mixing the physical aspects of the worlds in a confused tangle of terrain types—and also flooding strange colors of mana throughout every world. Behind the mana flows the urge for war, a product of both natural fears and the paranoiac murmurs of Bolas's minions.
The Conflux proceeds slowly at first. Each shard comes in contact only with its two planar neighbors, each one seeing a new color of mana from two strange lands. Suddenly each shard is fighting a war on two fronts, facing enemies so different from themselves, wielding magic formerly thought to be so impossible, that none refuses the call to war.
Naya faces an end to its celebrated tranquility. Knights and aven from Bant scout through Naya's forests, trampling the woodland paths and upsetting the migrations of the gargantuans. Dragons from Jund circle overhead, following the rivers of lava that burn new, blackened trails, and the footfalls of raiding goblins.
Guided by the visions of the elvish prophet Mayael, the elves, the Nacatl, and the earthshaking behemoths of Naya march to war with its new neighbors. In Bant they see a stifling imperialism, threatening to rein their jungle utopia under the yoke of a caste system. In Jund they see a cauldron of primordial savagery, a world not unlike their own but devolved such that life proceeds without respect, honor, or grace. The murmurings of the legendary Progenitus, deep under the Valley of the Ancients, whisper strange, dire truths into Mayael's visions, convincing her that war is a necessary evil to defend her paradise.
Invasion is a foreign concept for Naya's noble warriors and jungle celebrants. They've always revered the natural splendor of their lands, and yet now they must march out of them into strange terrain filled with frightening magics. For the first time they face spellcraft that can alter the mind or kill a living being outright. They only hope that their own nature-based magics, and their reverence for the gargantuans, can preserve them in the strife to come.
Bant's ruling Blessed caste face terrifying reports from their farthest frontiers. Esper's seas and etherium towers crash through rifts in Bant's shores, dredging in legions of metallic horrors. Naya's wild jungle encroaches, strangling well-tended orchards and engulfing border strongholds, bringing with it immense, untamed predators.
Bant's cultures take solace in a story-prayer about the legend of Asha, an archangel who gave her life to destroy the demonic menace Malfegor. Some believe Asha may even return one day—and now that the world seems made of enemies, the faithful hope that day is near.
The knight-captains of Bant soon realize that their time-honored forms of ceremonial combat have proven naïve. Instead of sending their champions out to meet their own exalted knights in single combat, the warriors and mages of the two fronts fight in massed armies led by titanic monsters, throwing chaotic and deadly spells with abandon. The angels seem powerless to enforce Bant's cherished law, and soldiers fall by the hundreds.
Esper's etherium supplies are running low. But as the shards merge together, the agents and mages of Esper see an opportunity to venture forth on a hunt for carmot, the red stone said to be crucial to the manufacture of new etherium.
But the Conflux brings Esper in contact with the boundless gardens and unenlightened flesh of Bant on the one side, and the horrid dregscapes and undead armies of Grixis on the other. Green and red mana encroach on the precision of the Esper landscape and foul the mages' efforts to perfect their world. The analytical vedalken see no way to interact with the brutish, flesh-loving beings of their neighbor-shards, and their gifts of precious etherium are spurned without a thought. The sphinxes decide that war is the only recourse, and legions of mages and their etherium-enhanced retinues press into the fray.
It's not long, however, before mages of the other shards discover that Esper's reliance on etherium is a point of weakness as well as strength. Esper armies are met with spells that target their filigree enhancements directly, crippling their power.
Grixis was a dying plane, a world feeding on its own meager living essence with diminishing returns, a world where humanity was going extinct. As the Conflux causes it to collide with Esper and Jund, the tantalizing energies of life—white and green mana—flood across the boundaries into Grixis for the first time in centuries. Long starved for living victims, the demons and undead horrors swarm into the adjacent borderlands like a plague, gorging on all the life essence they encounter.
For now, the "war" is nothing but a feeding frenzy for Grixis. Fleshcrafters slake their thirst for power by invading the sanctums of clueless Esperite mages, ghastly parasite-pets in tow. Vampires and zombie slave-drivers lurch into Jund, finding its reptilian predators unprepared for the vicious relentlessness of the undead.
Meanwhile, biding his time in a secret necropolis lair, the dragon planeswalker Nicol Bolas confers with his general, the abomination known as Malfegor. He bids Malfegor assemble an army of the most powerful necromancers and the most horrifying undead, and to demolish any remaining human holdouts he can find on Grixis. Malfegor knows that Bolas has deeper plans for this vast army of death, but for now, the elder dragon's true purpose remains unrevealed.
Jund was an ashen hell lit by dragonfire. Trapped in a cycle of predation, its warrior-clans, viashino thrashes, and goblin warrens all hunted one another, competing endlessly—only to have the winners die to carnivorous plants, reptilian monsters, or the whims of a ravenous hellkite. It was a plane in need of an exit—or at least in need of expanded hunting grounds.
When the shards merged, the rotten-flesh lands of Grixis overlapped Jund's primordial cauldron on one side, and the vine-infested jungles of Naya surged forward on the other. The goblin tribes of Jund began to explore the new lands, wondering whether they could find a place where they weren't the bottom of the food chain—but failing completely. Jund's scaly landwurms crashed into the adjacent shards, adopting both the lands of the living and lands of the dead as their new lairs. The warrior-clans found new frontiers of prey for their world-spanning Life Hunts, and the tyrannical hellkites found new threats to their dominion.
Jund's new enemies bear magics that its warriors scarcely understand. Grixis's black and red spells, and Naya's red and green, make sense in their destructive rage. But the transformation and perception magics of blue and the unity-encouraging and rule-imposing magics of white befuddle the predatory mind. In order to prevail in this new war, Jund will have to learn to think past its surges of instinctive hunger.