Family feuds can be deadly, especially when the two sides have armies. Research reported by Foreign Policy indicates that “countries are far more likely to go to war with other countries whose populations are genetically similar to their own.” The problem isn’t simply that genetically similar populations are close to each other. The trend holds true even when correcting for proximity by removing countries that border each other or are close together. Since genetically similar people tend to have more interaction, the research validates the old saw: Familiarity breeds contempt.
Source: Foreign Policy