Sorry that your faith in supranational organisations was so thoroughly squashed. It do be like that though. For a little while, Truman hoped that all nuclear weapons could be put under the control of the UN. Then that went belly up when the soviet union under Stalin learned how to build them. Theres always the IAEA though.
Truman never wanted that. He flew around knowing that his nukes gave him an advantage over the USSR. From this paper, it is clear that Truman wanted to maintain an atomic monopoly and as for Joint Chiefs of Staff, they didn’t want to share the nuclear secrets with any organization including the UN.