> In truth, effective ABM systems encourage a bolt-from-the-blue strike from the country without ABMs, because they fear the same from their adversary who might

> In truth, effective ABM systems encourage a bolt-from-the-blue strike from the country without ABMs, because they fear the same from their adversary who might be able to ride out a second wave, so theory says hit first. If leaders care more about surviving than about killing their enemies, then effective ABM (and defense against other nuclear threats) changes plans more for the country with ABM. If you try a first strike without ABM, you're dead whether your enemy has ABM or not (and if anything, you're slightly more dead if they have ABM). But if you try a first strike with a good enough defense, you might not be dead. And first vs second strike makes a huge difference, because destroying most of the enemy's nukes in a first strike is critical to making your defense possible. It might seem insane to launch a first strike if the defenses aren't perfectly reliable. (Or like, even if they are, since a first strike is certainly murdering hundreds of millions of people.) But during a crisis, if you think nuclear war is coming and might not be avoidable, then the math changes. In that case you're comparing your odds of surviving an enemy second strike to your odds of averting an enemy first strike. Then the ABM makes a big difference to your willingness to push the button. For the other nation, it might affect their perception of alarms (eg might make them think a false alarm is a true one, if ABM makes an attack seem more likely), and once that alarm goes off it might incentivize a larger or earlier strike to make sure that their vengeance is effective. But in my non-expert opinion it changes plans for the nation with ABM much more.