I know that shortly after the fall of the Soviet Union a large number of nuclear weapons were stationed within Ukrainian borders. However, it is my understanding that Ukraine never had control over those weapons. They were guarded and controlled by troops that were loyal to Moscow and Ukraine did not have the resources and expertise to maintain or operate these weapons. (Nor did they have the enrichment facilities to build new ones.) Is that correct?
When the soviet union fell into pieces some nuclear weapons stayed in Ukrainian territory and because the state what is owned them did not existed Ukraine owned them and with them Ukraine was the third largest nuclear giant in the world.
A hard diplomatic way led to there but on December 5, 1994 the leaders of Ukraine, Russia, Great Britain and the United States signed a memorandum in Budapest, the most importants are the followings:
And after they signed it Russia lent a helping hand to eliminate the weapons.
PS: Ukraine did not have the appropriate knowledge to possess these things and when the russians destroyed most of them were in very unsafe condition