In regards to Vikings and Spartans, etc, I would say there is appropriation here nonetheless, the appropriation of legacy. The whole notion of "Western thought" is an appropriated amalgam: we are not Greek (and many Anglo European cultures have reject the notion of Grecians being "white" to varying degrees, but we still use "deep time" to anchor ourselves, justify ourselves. In this way, we don't have to justify that we are "creating something new." Christianity may be the best case in point: it anchors itself to the ancientness of the Torah, yet contradicts its history at will, but this doesn't matter, the anchor remains.
The two can coexist. We can claim others' past glories as our own, and celebrate "our" own. (And in the cultural sense the conquering of the Americas is something that is celebrated, the overcoming of the "Indian as Other to the American self," as I once heard it put.