Over at the Diplomat I have some thoughts on modern arms races:
The traditional logic of the arms race is bound up in the security dilemma; what makes one state more secure makes its adversaries less secure. Even defensive measures such as a wall (or a missile defense system) can render potential foes insecure by neutralizing their offensive deterrent.
In large part because of the examples of the World War I naval spring and the Cold War nuclear buildup, we’re primed to expect symmetrical arms races, where one side purchases some number of X system, the other side attempts to build X+1, and hijinks ensue. Perhaps more commonly, differences in national interest and national capability produce asymmetrical races, in which the competitors try to counter each other through dissimilar means (air defense systems vs. bombers, for example). These races are potentially less destabilizing than symmetrical races, although much depends on the geopolitical context.