Historically of course Ukraine was part of the USSR and had about a third of their nukes . Problems with keeping - they didn't have a nuclear weapons programme so once the active elements passed there effective life couldn't esily be replaced . Other costs and practical problems .
My belief is the more countries that have nukes , the more chance some idiot does something stupid which effects us all . Putin is a case in point . Incredibly irresponsible to threaten . During the Cuban missile crisis one sub comander had a nuke torpedo loaded and both sets of numbers keyed and intended to use on a mistaken belief he was under attack - was only talked down with some difficulty by another officer .
These modern ICBM'S have multiple warheads and can hit many targets simultaneously . Would be reciprocated while in the air if aimed at any of the big 3 nuclear powers .