The Intervention is of two kinds. There are resource explorers, which nearly always represent one race, operating with great freedom and impunity, which are clients of larger powers. Sometimes, they are clients of independent trading networks that are engaged in illegal trade. Those resource explorers who have been in your world and who are in your world today represent members of this group.
Then there are Collectives, who are multi-racial, hierarchical and very well organized. Their worker classes are bred for specific purposes, and they are involved in collective breeding, which is a practice not all advanced races are engaged in.
The Collectives seek a more permanent residence in this world. They seek it as a world that either they or their clients could own and govern from afar, with human assistance. That is why such great care has been taken to study human psychology, human physiology and your reproductive process, as well as the biological hazards that exist on Earth. That is one of the reasons that plant samples have been taken and the world has been observed for such a very long time.
Passage from The Allies of Humanity, Book Three, Tools of the Intervention.