Columbus Day v Indigenous People's Day v Leif Erikson Day

Those Native Americans either assimilated (sometimes by force), or died. At the point of assimilation their history becomes our own, only then do I identify them as “us”, meaning part of the same nation that I belong to. Otherwise their history is ours only so far as our nations were allied or their actions influenced our history.

You are right on all points with this, but I would distinguish between history in the general sense and national history, and also between a commemoration or celebration and a national holiday. Reinforcing the national identity is an appropriate purpose for a national holiday, in my opinion.

~Max