Upbringing

This galaxy has some planets that are used to assist various forms of life through a certain stage of their development.

This is what your writer knows as Upbringing.
Our planet has been used for this function, over and over again, for millions of years.

Races evolve on other worlds and then are brought here by a group of races who work to assist the Progenitor race.  Progenitors  spark evolutionary leaps and monitor evolutionary development of new species and races. Once they reach a suitable point the Progenitors will ask one of their assisting races to relocate the species to a planet suitable for their Upbringing.
Often the race is aware of the reason for their location.  At times they are not but choose to go anyways. In some cases when dealing with hostile races this relocation is done by force and not invitation.

This planet has everything a race could need.  This is part of why our history is so confused.

Sometimes the race developing here learns to leave the planet.  Typically they will move on to a new world.

Sometimes they don't. Once they have reached a point where they are no longer progressing the are moved to a new world.

When the majority leave some often stay behind if they can, although sometimes the process required to reset the planet so she can return to her natural state.

Same applies on other planets used for Upbringing.

We have reached a stage in our Upbringing where we are at a crossroad.  It's about time we move on.  Still, there is work to be done first.  We can skip ahead and risk another cycle of control, or we can take a step back and correct our mistakes as to avoid once again falling under the control of others.  The Choice.
Specifically, we have to become a  sovereign race.  In order to do this we are going to have to overcome the Parents.  This is a task we are equipped but not yet prepared for.