The Rules of the Air were created under the Chicago Convention. The Chicago Convention, officially known as the Convention on International Civil Aviation, was established in 1944 and laid the foundation for international aviation regulations, including the Rules of the Air.

ICAO Annex 2 - Rules of the air
Historical background

The RAC Division, at its second session in December 1946 January 1947, reviewed Doc 2010 and proposed Standards and Recommended Practices for the Rules of the Air. These were adopted by the Council as Standards and Recommended Practices relating to Rules of the Air on 15 April 1948, pursuant to Article 37 of the Convention on International Civil Aviation (Chicago, 1944) and designated as Annex 2 to the Convention with the title International Standards and Recommended Practices — Rules of the Air. They became effective on 15 September 1948.