Ukraine used to have nuclear weapons - more than China, Britain, and France combined. It agreed to give them up in a deal in which the US, Russia, and the UK guaranteed its territorial integrity. It looks like it might have made a big mistake there, since Russia has violated its part of the deal and the US and UK are very unlikely to hold up their end of the bargain - and probably have no capability to do so.
Great power deals have a history of being worth approximately the value of the paper they are printed on, so this is hardly a surprise. The agreement in question was apparently not a formal treaty - such treaties being, in the US, the "law of the land" according to the Constitution, but the outcome to date should give even those bound by more formal treaties, like NATO, pause. NATO has six times the population of Russia, and sixteen times the GDP, so it hardly lacks for resources. Even without the US and Canada, it still dwarfs Russia on both counts, so the only question is whether it has the will to arm itself well enough to resist.
I suspect that one upshot of the Russian invasion is that no country will again voluntarily give up weapons of mass destruction, which is to say nukes, since the others hardly count. Gaddafi was dead not long after he gave up his weapons, such as they were, and Ukraine is another object lesson.