I probably mentioned this somewhere else on another thread but my memory will always and forever be crappy lol
If you remember Yellowfang's Secret, there was a scene where Molepelt warned Featherpaw.
"A long time ago, I was the ShadowClan medicine cat," he went on. "My Clanmates and I did a great wrong to another Clan—a Clan that belonged in the forest as much as any of us, but was driven out through our selfishness and hard-heartedness. I knew then that what we did was wrong, and I have waited, my heart filled with dread, for the Clans to be punished."
"Punished? How?" Featherpaw asked hoarsely.
"The time has come!" Molepelt's green eyes were wide, and he seemed to be gazing into the far distance. "A poison will spring from the heart of ShadowClan, and spread to all the other Clans." His voice became a soft, eerie wailing. "A storm of blood and fire will sweep the forest!"
Meaning, if SkyClan wasn't chased out to begin with, Brokenstar as well as Tigerstar, a SkyClan descendant, would never have been born. ShadowClan wouldn't be so broken, and the BloodClan and Dark Forest battles never would have happened. The entire Tigerstar bloodline would be gone, too. We would still have our twoleg problem. I'm not sure about the Darktail issue since it heavily depended on ShadowClan's loyalty, which could have changed with Broken and Tiger out of the way. Darkstripe, Blackstar...etc wouldn't have done much, they were either too spineless to cause trouble themselves or were forced to follow them.
StarClan—or Molepelt— has doomed the Clans over a mistake that was long forgotten. They (or he) had ruined the lives of several cats as well as killed countless others. This curse silently rippled throughout several generations, causing mayhem that never should have been started. No one even knew the existence of SkyClan until AVoS, and to this day absolutely no one knows about the curse. StarClan has no right to be doing what they did, it was far too late for that.