First nuclear weapons were used in 1945, almost 80 years ago. Today, out of ~ 200 countries in the world only 9 have nukes. Of those, only 4 did it after Non-proliferation of Nuclear Weapons Treaty. South Africa had them and gave them up under international pressure. Ukraine and other former soviet republics voluntarily gave them up after the breakup of the USSR.
So, yes. Unfortunately we still have nukes and there are way too many of them, but it's not like non-proliferation efforts achieved nothing. Iran, a large country with a lot of resources, has been trying to get them a for a while with no luck for instance.
And for frontier AI research you don't just need matrix multiplication, you need a lot of it. There's less than a handful of semiconductors fabs globally that can make the necessary hardware. And if you can't get to TSMC for some reason, you can get to ASML, NVDIA, etc.