I was listening to someone recently talk about the nations being God's plan from the beginning. His command to His people after the flood was to be fruitful and multiply, and to fill the earth. Filling the earth would result in geographic separation which would result in new language dialects, cultural separation, and genetic drift, since separated populations would be breeding with a small subset of the total gene pool. Perhaps there would never have been radically different languages, but the nations would have been born all the same.
So, the incident at the tower of Babel was not introducing the concept of nations as a mitigation of the evil of a unified people. It was introducing different languages to force the development of nations, which was His desire all along.
I'll amend this if I remember to whom I was listening when this became clear to me.