In April 2000, the Russian Duma finally followed suit. Forces to be destroyed will be deactivated by 2003. In 1972, the United States and the Soviet Union ratified a treaty that seems, at first, counter-intuitive. In the ABM Treaty, they agreed not to try to defend their entire territory against missile attack. In the logic of the nuclear age, this Cold War treaty makes sense.
Missile defenses encourage offensive force increases.
Both countries knew that missile defense, no matter how capable, could be overwhelmed by massive attack. If one country built defenses, the other would simply increase its arsenal, seeking to maintain the ability to inflict unacceptable damage on the first. Each country sought the capability to carry out, after an attack by the other, a substantial retaliatory strike. As long as that capability was preserved, each would be deterred from attacking the other. By agreeing not to build national missile defenses, the two countries sought to maintain deterrence while limiting and stabilizing the size of the other's arsenal.