I've only had a quick skim but what worries me is that the authors are investigating a fundamentally geographic problem yet don't apparently have a background in GI science. For example, the authors use fixed grid cells for analysis, yet the modifiable areal unit problem states that varying the boundaries of your analysis can change the result, and especially given the coarseness of their chosen grid I'd like to see at least some attempt to handle this (perhaps repeat with smaller/shifted grid cells, compare results), or failing that at very least evidence of awareness of the problem. I've an MSc is GIS and one thing I learned is that even with the best data and methodology (PhD level spatial stats) it can be extremely difficult to establish statistical significance, and I'm not convinced here. I'd like to see a far more sophisticated treatment of the GI science methodologically before the leap into the historical/economic domain. I strongly suspect the geo side would fall apart under close analysis, thus undermining everything beyond that point.