No : there's a great distinction between tribe and nation/ethny. Saying both are the same, just geographically different, is actually about projecting a modern western conception over a different concept (which lead to several mishandlement of the political/social situations in Americas or Africa).
For exemple, a tribe is tied by direct and known kinship, if more or less symbolic. A nation, on the contrary is tied by different features, the kinship being hugely narrative, and assumed symbolical.
Not distinguishing both is eventually coming down to refuse tribal structures and groups their own specificity, treating them as only a variant of OUR own. At some point, eurocentrism should be really nuanced.
I think the development of nationalism and nation-state really played a part, then. With the development of nationalism in the 19th and 20th century you saw people's identities moving away from the local to the nation. As such, the local ethnic 'tribal' (for lack of a better term) identity was augmented and then surpassed by the national. OF course, standardized language, education and the like all played a part in this.
Its a bit of a broad argument, and there are many variations, but I think it makes some sense.