This is mostly wrong. For a period accuracy on ICBMs wasn't very great (on the order of a kilometer), which is why they made use of very high yield weapons in

This is mostly wrong. For a period accuracy on ICBMs wasn't very great (on the order of a kilometer), which is why they made use of very high yield weapons in the several megaton range. Large warheads were necessary to take out targets (such as population centers) with those accuracy levels. Then several things changed: accuracy improved greatly, the ability to put multiple warheads on a single missile arrived (MIRVing), and anti-ballistic missile defense (ABM) started taking off. This lead to the use of more, higher accuracy, lower yield warheads to take out targets. You could blanket a city with sub-megaton MIRVed warheads instead of using one big 10 megaton bomb. And then the calculus of "but how many will be lost to the ABM systems?" came into play, which resulted in use of "penetration aids" like decoys as well as the deployment of vast numbers of warheads to ensure enough of them made it through. That led to a massive rapid escalation in warhead deployment during the '60s and '70s until the ABM treaty flattened it out. But this is only half the story. The other half is the massive deployment of tactical (battlefield) nukes. With the invention of smaller nuclear warheads combined with the massive production capability of the weapons procurement pipelines in the US and USSR it became possible to deploy tens of thousands of tactical warheads. These would be used for everything from anti-ship missiles and torpedoes to anti-aircraft weapons to short range ground strike missiles. The late Cold War and post Cold War arms limitations significantly reduced the deployed number of warheads of both the US and USSR. They massively curtailed the number of tactical nukes deployed, and they resulted in a lot of "de-MIRVing" of missiles. A modern Ohio-class nuclear missile submarine can carry 24 missiles each of which can carry up to 12 W-88 (475 Kt) warheads. Potentially that's up to 288 warheads and over 130 megatons of total destructive power, basically WWIII in a can. However, today they carry far fewer warheads than that due to treaty limitations. Similarly, most of our land based ICBMs have been de-MIRVed and we've retired new weapons systems (like the MX/Peacekeeper) which were heavily MIRVed. All of this has translated into far fewer warheads in service or on alert and a much reduced overall destructive capability. It is still an overwhelmingly enormous nuclear destructive capability but it has been reduced significantly through treaty obligations over the years.