Humanity poses a major problem for most other races in the galaxy.
Most known species had a period of unification before they achieved sufficient technology and resources to make the jump outward to the stars. As such while there are variations within most sophonts they tend to share a common cultural base from which they derive. not so with humanity.
Herein lies the problem.
Humanity's jump to the star came about mostly due to the efforts of Largo Eximus and his effort to do an end-run around political and economic power blocks dedicated to their hold on mankind to their own benefit. This series of conflicts between the man who would eventually become Emperor is central to many questions historians have posed about his early years and the source ot the leverage he used to drive forth his agenda of taking Man to the stars.
Why, when all evidence points to his being born in the Western United States did he develop his first base of operation in Africa? Why are the ten oldest starports on Earth built outside the borders of the most technologically and economically advanced country on the planet at the time? If asked today the Emperor will most often give a quote along the lines of a prophet not being accepted in his own home and not elaborate.
But this lack of unity throughout most of his early career gave rise to the problem of humanity not having acquired a common cultural heritage that most other races have attained before they made the great jump. this was exacerbated by Largo making efforts to separate the most contentious groups by setting up cultural colonies in an effort to give them room and time to, as he often put it, grow out of a need to slaughter each other.
Now not all such colonies grew out of violence. Some were established to allow a number of cultures from being forced out of existence due to various advances. The best example are the three Amish colonies of New Goshen, New Cannan, and Prosperity. The colonies were funded by the Emperor to preserve what he called an important and significant cultural relic that was in danger of dying out due to an increasing impossibility of resisting change brought on by constant exposure to the outside world.
In all close to 50 cultural enclaves were given colonization charters in the first century after the Jump. The resulting lack of cultural unity makes humanity confusing and unpredictable to most of the species we share the star lanes with.
As a Side note...
from this point going forward, I will abandon the timeline method of charting the histories in favor of telling the individual stories.