Endwalker is the most controversial expansion

[Shurrikhan]

The War of the Magi predates the modern city-states of Eorzea by about four hundred years.

And Allag, also mentioned (just two sentences after), predates them by two Umbral Calamities more, no?

Yet, I wasn't aware the latest set of civilizations had to be present for something to be part of the history of the same continent?

Eorzea isn't just a body of 6* "civilized" nations (and many others outside that descriptor). It's... also the continent itself, with more than 12 eras of history -- the continent on which, yes, the War of the Magi took place, and from which the Allagan Empire started its conquest outword.

* Ishard, Ala Mhigo, Sharlayan, Gridania, Ul'duh, and Limsa Lominsa, with two others only pretty recently having dropped from the count.

Those historical mentions don't seem a warrant for "modern Eorzea deserved whatever the Garleans threw at them*," mind you -- only that the Garleans are far from some outlier, even compared to just the events seen on Eorzea itself, let alone the wider world.

* Though, yes, the majority of our citystates were frequently amoral perpetrators of war crimes and the pogrom-equivalents, spent time as despotic theocracies, etc.