Smaller countries like China and India? Population-wise they're larger, and area-wise they're not two orders of magnitude smaller. My point is that the chart doesn't really show nukes "spreading around the world" but concentrated almost entirely in two countries. Maybe the US policy did nothing to help it, but for all we know there would have been plenty of other countries with thousands of nukes as well without it. I'm not arguing that the policy was effective or not, just that I don't see how that chart is enough evidence alone to conclude one way or another.