The straighter a nation’s borders, the less successful the country, according to a working paper (.pdf) by three professors (two from Harvard and one from NYU):
Artificial states are those in which political borders do not coincide with a division of nationalities desired by the people on the ground. We propose and compute for all countries in the world two new measures how artificial states are. One is based on measuring how borders split ethnic groups into two separate adjacent countries. The other one measures how straight land borders are, under the assumption the straight land borders are more likely to be artificial. We then show that these two measures seem to be highly correlated with several measures of economic and political success.
Clearly, Iraq has the bubbling cauldron of three different ethnic groups, but how straight are the country’s borders?
Note the near ruler-precision of the southwestern border. For comparison, take France, a relatively stable nation with squiggly borders all around: