The Neo United Nations (NUN) is an international organization established to maintain worldwide peace and cooperation. It is the parent organization of the Universal Peace Enforcement Organization (UPEO), which enforces the NUN's stated purpose.
Following the rise of both General Resource and Neucom Incorporated, as well as increasing tensions between the two companies, the NUN became more involved as an intermediary for the companies in the 2030s, attempting to de-escalate their continued disputes.
In the Nemo simulation, the NUN's efforts fail as all-out war breaks out between the two companies. The NUN attempts to host peace talks in Cape Rainy, but the talks are suspended when the personal plane of Gabriel William Clarkson, the representative of UPEO, was attacked.
- The NUN may have been retconned as the IUN in Ace Combat 04: Shattered Skies and Ace Combat 7: Skies Unknown. This is supported by the 25th Anniversary Wallpaper, where Typhoons with UPEO's livery and "EC071" identification code sport IUN marking on their vertical stabilizer.