Columbus Day has EVERYTHING to do with history: the struggle over the meaning of the past determines how we think of the present.  The discourse of history is always already politicized. Social forms, including nations, that people assume to be normal and natural are really a kind of historical accident. Reality itself is historically contingent.

Complaints about how revisionists are "dividing us" are really just cries of anguish as the assumptions that support certain historically contingent visions of reality are debunked and demystified. In other words, the "divisions" have always been there; it's just that they always benefitted those on one side or the other, and so were assumed to be normal and natural by the beneficiaries.

Any number of examples of this could be adduced: the "discovery of America" by Europeans, the Puritan vision of the "city on a hill" as a model of American nationhood, Manifest Destiny, American exceptionalism, white supremacy, etc.