Intervention was when the Homeworld interacted and influenced the lesser species.
After the Imperator Presidency, attitudes towards intervention led to fractures in Homeworld society. Some like the Order of the Weal considered it the greatest threat, some thought they should employ diplomacy, and others that the lesser species should be controlled. A pro-interventionist group even set up their own temporary Homeworld on Dronid.
Ironically, before the War the most prominent interventionists excised themselves from time and became the Celestis (PROSE: Intervention)