When states compete with states, the “individuals” that confront each other are rival governments, and the relevant weapons their respective military forces. New states are born from time to time, and other states disappear, but this isn't the evolutionary turnover that matters here, because arms races between states happen much faster than this, beginning and ending during the political lifetimes of the involved states. Rather, it's the military establishments within each state that grow or recede. Circumstances conspire to spark an arms race when rivals face each other in such a way that bigger militaries suddenly become much better than smaller ones. The state with more or better weapons gains an advantage that prompts the other side to catch up, launching them both into increasingly extravagant back-and-forth cycles of military spending. … For political arms races, the best parallel with animals is not the gradual turnover in populations we've focused on thus far, but rather a confrontation between two rival males—two crabs, for example, that face off in the sand. Who will back down? An arms race between states erupts in the same way a contest between crabs escalates; neither yields, pushes give way to grabs and jabs, grappling to smashing, and then pounding, and finally unrestricted war. When it comes to warfare, states behave just like crabs on a beach.

Emlen, Douglas J, Animal Weapons_ The Evoluti…, loc. 553