What stops countries from using nukes?

TL;DR

Nuclear deterrence works through credible retaliation, dispersed weapons, and deliberately vague red lines that keep enemies guessing.

Key Points

• 1.Credible launch authority is the first pillar of deterrence. The US president alone can authorize a nuclear strike within 5 minutes using special codes and the 'nuclear football' briefcase, which contains a phone and a target list showing projected casualties.
• 2.The nuclear triad ensures survivable second-strike capability. The US spreads nukes across underground silos in the American heartland, aircraft stationed globally, and submarines carrying up to 20 missiles with multiple warheads each — making a disarming first strike nearly impossible.
• 3.Intentionally vague red lines are the psychological core of deterrence. Rather than declaring a clear 'no first use' policy, the US and Russia keep thresholds deliberately fuzzy to deter not just nuclear attacks but also chemical weapons and conventional aggression.