Noah's First Rule of Conflict

...is that people or groups are more likely to fight or compete against other people or groups that are more similar to them. Similarity breeds conflict.

Now there's some data to back up my rule:

We found that populations that are genetically closer are more prone to engage in militarized con?icts and wars with each other, even after controlling for a wide set of measures of geographic distance, income differences, and other factors affecting con?ict, including measures of bilateral and multilateral trade and differences in democracy levels. We also provided a theoretical model of con?ict and relatedness that is consistent with these results. In the simplest version of our model, populations that share a more recent common history have had less time to diverge in preferences and characteristics that determine the set of common issues they care about, and over which they are prone to fight.