The "deal" about nation-building refers to the fact that our view of the Gauls, the Germanics, the Romans etc. is as much based on our own research as it is based on traditional prejudices, visions of these peoples we have. Most of those visions (or legends) were made up during the evolution of national states from the 15th to the 19th century. Even those states were primarily based on a common language (like France, Italy, Spain etc.). Ideologically, common heroes were found - El Cid in Spain, Charlemagne and Vercingetorix in France, and even the intelligentsia among the shattered quilt of states among German speaking countries nurtured their heroes like Arminius/Herrmann and Friedrich Barbarossa. Those heroes were celebrated in arts, poetry and literature, endowed with the traditional three cardinal virtues of justice, valor and modesty, while their opponents (members of other nations mostly) were assumed quite the opposite.
These legends were spread among the nation, and they also slowly found their way into the minds of members of other nation. For a very long time nobody considered the element of propaganda in those made-up legends. Hence, those national heroes were used as achetypes of freedom fighters all over the European-dominated world.
We still have those visions in our minds, because we are partly products of tradition. The point is, we have to reveal reality from the fog of those visions - stop seeing Germanics either as drunken rapists resting on boar skins is just a beginning. The postulation of the river Rhine being a border that completely divided Europe politically and culturally during the Roman empire is another myth.
I refer you to

• Barry Cunliffe: The Ancient Celts, OUP Oxford/New York 1997, pp.1-19 (Visions of the Celts)
and
• Germanen, Germania, Germanisch Altertumskunde, ed.by Heinrich Beck, Heiko Steuer, Dieter Timpe & Johannes Hoops. DeGruyter Berlin/New York 1998.

Long post ... sorry. Hope it helps. :o)