The Geography of Genes

One can imagine that past cultures occupied geographically discrete areas, meaning that, genetically, you would be more likely to be more closely related to the people within your cultural group than those outside it. However, with the advent of modern transportation, gene flow between individuals of spatially separated groups is more likely than ever before. Given this, would people from various countries cluster into genetically similar groups? A study by Novembre and colleagues used a PCA on a sample of individuals genotyped at 500,568 loci, and revealed that not only did people of different European nationalities cluster into descrete groups, but the spatial structure of the clustering also resembles the political boundaries of Europe. If the ancestry of modern human populations (at least in Europe), reflects national boundaries, would it be possible to use aDNA to reconstruct the spatial boundaries of past cultures?