"The Budapest Agreement required Ukraine to eliminate the strategic missiles, missile silos, and bombers on its territory and transfer the 1,900 nuclear warheads to Russia for disassembly. Ukraine was the third-largest nuclear power in the world. They had more nuclear weapons than China. In return, Ukrainians gained guarantees that the United States and Russia, joined by Britain, would provide security assurances. The Budapest Agreement committed Washington, Moscow, and London, among other things, to “respect the independence and sovereignty and existing borders of Ukraine” and to “refrain from the threat or use of force” against that country.

Belarus also agreed to surrender all nuclear weapons as part of this agreement, but it had only mobile missile launchers at the time. Kazakhstan was the third member of the Agreement and chose to return the nuclear warheads and missiles to Russia.  Ukraine was reluctant and wanted to keep some of the nuclear weapons. There was a side agreement between the Ukrainian and Russian governments whereby giving up Ukrainian claims to the nuclear weapons and the Black Sea Fleet were surrendered on the basis that Russia gave $2.5 billion in gas and oil debt cancellation and future supplies of fuel for its nuclear power stations. Ukraine did not want a commitment to transfer all warheads by June 1st, 1996 to be made public for local political purposes while Russia did not want the financial compensation for uranium made public concerned that Belarus and Kazakhstan would also demand free fuel."
Did Incompetence Set in Motion The Ukrainian Crisis?