Why did the salt talks place extra emphasis on anti ballistic missiles?

The SALT (Strategic Arms Limitation Talks) negotiations placed extra emphasis on anti-ballistic missiles (ABMs) because these systems could significantly undermine the principle of mutually assured destruction (MAD) by providing a defense against incoming nuclear missiles. The fear was that if one side developed effective ABM systems, it could lead to an arms race, as the other side would seek to enhance its offensive capabilities to overcome the defense. By limiting ABMs, the talks aimed to stabilize the nuclear balance and reduce the incentive for either side to escalate their nuclear arsenals. This focus was crucial for maintaining strategic stability during the Cold War.