The Coalition of Nations is a theoretical framework of a "brotherhood of civilized nations" that would arise in response to horrible atrocities or a shared existential threat. While there is no formal organization in place, it's a popular idea among those valuing collaboration, a stable political landscape, and open borders.
The idea started with the Umvarin Conference, with one spectator later commenting that it was a "shared alliance against [...] evil". The temporary brotherhood between people who would've never met otherwise in The Splintering left a powerful impression in the heads of those that participated. The coming Age of Chaos and the years of hardship after mostly dissuaded those starry-eyed ideals, though there were a few scattered philosophers and thinkers who believed in the idea.
The idea would rise to prominence with the Age of Frost. The romanticism that came with nearly the entirety of the north and the south of the Continent uniting to fight a shared threat of devilish necromancers and evil undead was enough to kickstart the philosophy again and not only bring it back into the realm of public thinking but bring it to new, never before seen heights. While no formal alliance was ever signed, there was an informal peace and cooperation between the armies sent to pacify the northwest brought about by the threat of the Armies of Dread.
After the Age of Frost, Grandmaster Benjamin Halen of The Order would attempt to bring the Coalition of Nations into existence, but the initiative failed due to a lack of will from most nations to sacrifice their power for some nebulous and undefined goal. The peasantry were much too focused on trying not to die to get caught up in the idea of any sort of national politics while nobles saw the idea as something that could undermine their authority and thus opposed it vehemently. Merchants across the Continent were one of the biggest supporters of the philosophy as it would stabilize the world, allowing for more trade and more effort spent on crushing bandits, one of the major causes of merchant deaths. Despite this support, merchants alone hardly had any sort of serious political power they could throw around to pressure anyone into the Coalition of Nations agreement.
During the era after the Age of Frost, the romanticism surrounding the idea of a Coalition of Nations mostly shattered during the long years with little validation for the idea. Without any core tenants or unifying ideals the philosophy faded away, with most dismissing it as a thing that would happen far in the future in a utopian setting, one far from the current day.
With the advent of the Blood War, however, that changed. With the outcry produced by the uncovering of The Blood Mages cabal controlling Uthan and the plot to launch a conquest of the Continent there was a sudden wave of new talk about a Coalition of Nations that was reinforced by the joint declaration of war from nearly all civilized nations against Uthan. Optimistic thinkers hoped that this would be the breakthrough needed to finally produce a Coalition of Nations.
After the war, the Treaty of Teckitan was the foundation for this Coalition of Nations, though not to the extent that most supporters wanted. While it did acknowledge an international community, it made no further efforts to bind them together outside of reparations for the war.
For now the idea of a Coalition of Nations seems a far-fetched idea that comes tantalizingly close to fulfillment but always inching away when they reach the edge.