1922 is considered as the year in which air traffic control began. The first internationally agreed rules were drafted in 1919 by the Commission Internationale de Navigation Aérienne (CINA). They were ratified by 10 countries in 1922. The first mid-air collision between two commercial airliners over Normandy (France) in April 1922, further encouraged the UK, France, Belgium and The Netherlands to implement guidelines for keeping aircraft separated, thus forming the basis for air traffic control as a service to avoid collisions.
More details at: https://www.atc100years.org
