Nation-states cannot, in my mind, be compared to individuals when it comes to propensity for aggression. The vast majority of individuals, in, say the U.S. are

Nation-states cannot, in my mind, be compared to individuals when it comes to propensity for aggression. The vast majority of individuals, in, say the U.S. are not armed, whereas the majority of nation-states have a military. Furthermore, the countries that are in proximity to "aggressive" states either have a strong military e.g. Israel, or have military presence from other countries with strong militaries e.g. South Korea. Also, the distances between different countries vs the spread of information is also vastly different. It is harder to commit an international act of violence with no witnesses than it is an interpersonal one, and the threat of retaliation keeps violence at bay, for the most part at least.