The Great Retcon implied the removal of Dominion's backing lore. It's fundamentally a League story, and one of the better ones, IMO.
Our last, best hope for peace
Kalamanda was the moment of truth for the nascent League of Legends, founded as Runeterra's last, best hope for survival after the Rune Wars. Demacia and Noxus occupied the site of a new nexus. They both wanted it quite badly, and they were both (it seems to me) growing resentful of the League's diplomacy and bureaucracy. The League tried to mediate, but a clash between Valoran's two superpowers was something it was not well equipped to mediate: it was utterly dependent on them both for its strength and legitimacy. If either one of them walked, the League would collapse, or at best turn into a military alliance for a war against the other, which would in turn likely destroy Valoran with the "fallout".
(Some people may no longer recall, this long after the retcon, but the basic idea was that "rune magic" was essentially a magical WMD, a means of channeling unimaginable power that also inflicted grievous damage on the arcane foundations of Valoran. Whereas nuclear weapons have MAD going for them, and any one country pushing the button would trigger an apocalypse, it was a more gradual process with rune magic…any given use of rune spells was not obviously going to destroy the planet, and it was instead a gradual, ecological phenomenon. There would presumably be a breaking point, but it was not a binary proposition, leaving MAD of little use.)
Kalamanda was Valoran's worst nightmare for the future
Let's emphasize this. You've got Valoran's two superpowers. They've deployed troops within rock-throwing distance of each other. And it's all on top of a nexus. You know, those massive conduits of arcane energy. You could not construct a more dangerous scenario, in terms of likelihood of triggering another Rune War. Oh, the fighting in itself was not an apocalyptic threat. People fought all the time. As long as both sides obeyed the League's rules about rune magic, and contained the fighting within certain boundaries, it was something that could be handled by ordinary diplomacy and maybe some League matches.
But Kalamanda was exactly the sort of battle that could never be contained: it had to be all or nothing. Within five minutes of swords being drawn, one side or the other would bust out their runespells, call in their Summoners (well trained after all that time at the Institute), and unleash absolute hell on the enemy. Because with that much energy right at their feet, virtually every other tactical consideration was irrelevant. Because otherwise they'll do it first. And because whoever won this battle would go into the coming Rune War with a brand new nexus to power its spells. Sure, moderates argued, sooner or later, probably sooner, that nexus would blow them all sky-high, and then it would be anyone's guess what exactly would happen to Valoran: Void invasion, from a rupture in the dimensional fabric? Undead apocalypse, after the veil between life and death is torn apart in the manasurge? Elemental realignment of Valoran's leyline network, setting the whole continent on fire, or freezing it into ice (Lissandra hype)? Maybe it would just blow the damn planet up; it was being held together by duct tape and fervent good wishes after the last Rune War anyway. Or maybe they'd get REALLY lucky and it would just be another decade of all-consuming warfare, followed by one of these more final conclusions. But the people calling the shots weren't interested in listening to these magical environmentalist types. "We cannot allow a mineshaft gap!"
So the League tried to calm them both down: hey, what about this? We have this quirky idea for sharing the nexus. Or maybe nobody gets it? Or how about we form a committee? Let's talk about this! What do you think about arbitration on the Fields, huh? Best of five? We've got some new items!
And then Demacia and Noxus finally told those ideologues and politicians in the League to get lost.
"The League was our last, best hope for peace. It failed."
https://www.youtube.com/watch?v=d9EbGd1AlMg
Obligatory Babylon 5 clip. Dun dun DUN! Dun dun DUN! Dun dun DUUUUUN!
Demacia and Noxus came to blows. The war was on. One can only imagine the panic that spread through Valoran when the news hit. The founding of the League had given Demacia and Noxus decades to prepare for the next Rune War, and many cynics believed that this was in fact why they decided to create the League in the first place. They had been building up their arsenals, and training their Summoners and Champions, for this war to end all wars.
The League had a terrible decision to make. It could sit back and hope that Demacia and Noxus would come to their senses before it was too late. Or it could intervene. Its intervention would be largely symbolic: even with all their magic, the notion (unfortunately echoed by some after the Retcon) that they were all-powerful puppetmasters is neither a good creative choice nor one supported by the JoJ or other prior lore. The League could not truly stop a war between Demacia and Noxus if those superpowers wanted a war. But the League could buy a moment of peace, creating a last chance for diplomatic resolution, and it could send the symbolic message that if these two wanted armageddon they'd do it over the smoldering ruins of the Institute. And that was the problem: it was entirely possible that Demacia and Noxus would take this as the last straw, and that it would be the end of the League.
The League takes Valoran back from the brink
The League chose to act. They gathered together enough magic to forcibly halt the immediate fighting between Demacia and Noxus. This was surely a startling development. My preferred analogy is to a pair of people who get in a fight outside a bar, and just as they pull out knives, their mutual friend steps between them and says, "no, come on, don't do this." If they truly want to fight, they'll throw the friend aside and go at each other. But it also gave them one last chance to avoid what was otherwise inevitable.
It worked. Demacia and Noxus took a long look at each other, and decided that they weren't going to fight this fight just yet. The League had proved it was more than a mouthpiece or political forum for the great powers of Valoran. And the lesser powers saw that when the chips were down the League was willing to put itself between even Demacia and Noxus to prevent another Rune War.
Suddenly, the League didn't seem like such a joke any more. It had been ridiculed as window-dressing for a temporary cease-fire, or perhaps a "peaceful" means by which Demacia and Noxus could arrange their allies and pawns for the next big fight. But it had just brought Demacia and Noxus back from the brink. And hey, if the League could deal with Demacia and Noxus engaged in combat atop a nexus, maybe it wasn't so absurd to think it could deal with a border incursion, or an argument over taxation, or the Noxian invasion of whatever Noxus decided to invade next.
Maybe, people began to think, this League might stick around for a while after all.
Kalamanda is a League story.
I think it's an awesome story. Political intrigue, action, drama, magic…it's chock full of potential. And a fantastic example of how the League works (worked? nah, works) as a storytelling element.
But, of course, it's all built on the League. You can't just "remove references to the League" and keep the same story. Unless you, I don't know, invented some brand new third-party entity that was trying to mediate peace between Demacia and Noxus. And had a lot of mages who could do a timestop. Gosh. You could call it like…an Alliance of Champions. Or a Council of Heroes. Or a League of…something beginning with an L.