The Frontier Awaits
It has been forty-three years since humankind discovered the Zero-point Drive. Practically overnight: the energy crisis that had become the wedge between social castes - solved, the dependence on earth and its colonies for the means of survival - surpassed, the gates of the future - opened.
Those with investments in the power structures of old needed a new ploy, a new "noble hardship", to keep the common mans interest firmly in the struggle and not in joining them in luxury. The answer came with a distant signal. A message of recognition, of hopeful alliance from a distant corner of the galaxy. Aliens were not only real, but numerous it seems - and while they had been hesitant to reveal their presence to the primitive and warlike humans, that revelation was now an inevitability.
With the help of alien designs, man built its first interstellar vessels and left the Sol system to meet their neighbors. Those to take the first Zero-point jumps (ZP's or Zips) were greeted with a society not wholly unfamiliar. The meeting ground of inter-species politics and trade, known as The Cave was rife with the same ambitions, aspirations and moral failings humans had always known - but it took them some time to suss this out through the varied eccentricities and social approaches of the galaxy's developed races.
Back home, the explorers were treated as heroes in the press and the aliens given a god-like or villainous depiction as the politicians needed them to be. ZP energy stations became "known dangers" for the effects they caused on life when used in-atmosphere and targets for regressive terrorist groups, such as The Fortunate Fate who drive to take human life back to a Sol-centric existence.
The member species of The Cave's ruling council each have different, and not usually pleasant views on the newcomers. Even those who can hearken back to the frontier spirit humans display have largely put such impulsiveness aside in favor of more reliable interactions. That is not to say they see no use in accepting the humans - any race willing to fight itself to the brink of extinction so many times - so unnecessarily, and that soaks up technological instruction like the earthlings is an obvious and natural fit for military work.
That is where you will find most post jump earthlings: The Cave Defense Force, various mercenary bands, or personal enforcers for open or "dark" dignitaries. Only now, decades after making contact, are earthlings making headway into more peaceful economic and social roles.