The New United Nations was an organization in the 21st century, replacing the United Nations by 2036.
In 2036, the NUN declared that "no Earth citizen can be made to answer for the crimes of their race or forebearers".
The alliance had collapsed by 2079, during the post-atomic horror in the aftermath of the Third World War. (TNG: "Encounter at Farpoint")
In 2328, the SS Mariposa had a United Nations registry of NAR-7678. (TNG: "Up The Long Ladder", okudagram)