What ended the XB-70 was SAM's, not ICBM's so much. It was much easier for the Soviets to build and deploy the SA-5 Gammon (aka the S-200 Angara, basically a pe

What ended the XB-70 was SAM's, not ICBM's so much. It was much easier for the Soviets to build and deploy the SA-5 Gammon (aka the S-200 Angara, basically a perfect a B-70 killer) than it would be to build and operate a significant fleet of B-70's. This was actually so clear to the USAF that about five years after the B-70 was canceled (about the time the first XB-70 took flight), when the Soviets actually started to deploy thousands of SA-5 across the Soviet Union, the USAF was convinced it must have ABM capabilities. It wouldn't make sense for the Soviets to use ~10% of their annual concrete production to defend against a threat that the US had already canceled, so they thought that the SA-5 had to be a super-useful national ABM capability (they had already evaluated that the ABM-1 system under construction around Moscow, the so called Triad system, as overmatched by the existing Minuteman I deployments, but thousands of missiles required more even more thousands of warheads to exhaust). In response, the USAF suddenly expressed significant interest in MIRV technology, and the Minuteman III program began, and ICBM warhead numbers started to get really insane. Cite: https://www.thespacereview.com/article/3677/1 https://www.thespacereview.com/article/3677/1