Project Sapphire

On a basic level, Russia simply lost access to large quantities of nuclear material.

For example, if you watch the Netflix documentary Turning Point on the Cold War, you'll learn about something called Project Sapphire, a desperate effort to recover enriched uranium from Kazakhstan that locals were selling from literal open buckets after the country fell out of Soviet control.

But Russia didn't just lose the nuclear material.

Arguably more importantly, Russia lost the expertise behind those warheads, the expertise behind both their creation and their maintenance.