I think you meant "includes" or "implies" instead of preclude, but I generally agree with this. The only instances where empires are not acquired through some sort of violence, I think, are either through union of royal families (which often still don't quite reach a state of imperialism absent additional conquest), or by claiming completely unsettled territory (and even then really aren't empires, but we still include civs like the Maori absent any better example of imperialism in the region).
Re: The Navajo
Soooooo my hopes about the Navajo are a bit muddled at the moment thanks to a recent trip to northern Arizona. Apparently the Navajo nation is expressing an extremely high infection rate with the current pandemic, and has a higher infection rate than the state of New York. This phenomenon is largely unique to the Navajo and isn't happening on other reservations like the Yavapai, Havasupai, Tohono O'odam, or Apache, nor even in the Hopi reservation which lies wholly within the Navajo reservation. Apparently the Navajo government is trying their best to implement and emphasize the importance of pandemic procedure, but the tribe members are mostly neglecting to social distance and wear masks. Worse, instead of quarantininng and seeking proper medical care, many are participating in healing circles. I.e., they are getting together in their hogans and intentionally breathing the same circulating air.
Given that I and I think others were hoping for a Navajo nation with a hogan UI that would incorporate a plague/pandemic mechanic, specifically functioning as a healing house, this development disheartens me. It would feel, at minimum, insensitive at this point to implement a Navajo civ that represents hogans as an anti-pandemic mechanic when in reality they have precisely the opposite effect with respect to respiratory contagions.