Warhammer 40,000 is the world that emerged after Gaia's forces lost to the WyrmThe Gaia Garou and other changing races failed in their attempt to defeat the Wyrm, who proceeded to subjugate Earth and the rest of the galaxy. The Space Wolves are kinfolk descendants of the few Garou who survived, but they are ignorant of their true heritage. The Kroot are descendants or a few surviving Corax who fled to far-flung planets, where evolution made them capable of normal biological reproduction and evolutionary cannibalism. Spreading Wyrm-taint is compelling sentient beings to engage in war, depravity, and greed. The overcrowding, pollution, and ecological devastation is also the result of Wyrm influence, just as it was for Gaia. Already insane due to its confinement in the Weaver's web, the Wyrm's various aspects gained full sentience and autonomy. Beast-of-War became Khorne, Eater-of-Souls became Nurgle, and Defiler splintered into Slaanesh and Tzeench. Wyrm spirits, now called Chaos Daemons, thrive in the Umbra, now referred to as the Warp.
Wyld is behind everything.Probably Wyld wants Weaver and Wyrm to destroy each other for whatever reason.
Wyld couldn't stop Weaver from imprisoning Wyrm not because he didn't care but because Weaver imprisoned him somewhere first.This makes situation even worse.
Wyld is trying to compensate for the WyrmWhen the Wyrm went insane, it couldn't perform its duties properly. In a misguided attempt to maintain balance in the cosmos, the Wyld is trying to carry out the Wyrm's destruction duties itself. Wyld has thus assigned tasks that involve killing large numbers of humans to Wyld-aligned races such as the Rokea, Ratkin, and Red Talon Garou. However, because the Wyld is acting outside of its M.O., it executes these tasks imperfectly and just makes the cosmic imbalance worse.
Gaia did not assign tasks to the Changing Breeds.Gaia did not assign tasks to the Changing Breeds; rather, she haphazardly created them with no original purpose. In other words, the Gurahl were not created to be intrinsic healers, the Garou were not created to be intrinsic warriors, etc. Rather, the different races were assigned these tasks by their totem spirits, each of whom had an agenda. Each race molded its culture accordingly and sought out spirits who would teach them the desired gifts. Conversely, some of the Changing Breeds made up stories about their Gaia-given missions to justify their actions. For example, the Ratkin made up stories about their duty to cull excess humans to justify their savagery and hatred toward human society. Nuwisha dislike the Garou and enjoy giving them a hard time, so they made up stories about their supposed cosmic role as trickster mentors.
The real reason for the War of Rage is the Red Talons' insecurity.The War of Rage was a campaign of genocide where the Garou tried to exterminate all of the other Changing Breeds. Its most fervent proponents were the Red Talons, who all Lupus-breed (born as wolves), and consider themselves the most "pure" tribe because of it. Their philosophy involves a lot of "wolves are Gaia's Chosen, and humans are not special." But the other Changing Breeds aren't part wolf, they are all part human. Their existence is a reminder that the Red Talons' claims of wolves being Gaia's Special Favorites is a load of self-aggrandizing lies. The solution? Wipe out all the other Changing Breeds, eliminating the proof that if one species is Gaia's chosen, it's humans.