The United States developed its nuclear weapons policies early in the Cold War—some 60 years ago—and they were shaped by the weapons technologies of the time. These technologies have changed radically since then, but the United States has not modified key nuclear policies to reflect those changes.
In particular, the United States continues to field silo-based nuclear missiles and keeps them on high alert so they can be launched quickly on warning of an incoming attack—creating the risk of a mistaken nuclear war in response to a false warning. Yet, the original rationale for intercontinental ballistic missiles (ICBMs)—and for keeping them on alert—no longer applies.
Wright, David, William D. Hartung, Lisbeth Gronlund. 2020. Rethinking Land-Based Nuclear Missiles: Sensible Risk-Reduction Practices for US ICBMs. Cambridge, MA: Union of Concerned Scientists. https://www.ucsusa.org/resources/rethinking-icbms