Humanity reached from the womb Earth and slowly spread across the Galaxy. As with all human history, the expansion followed cycles of growth and decline. Humanity eventually met other sentient species and struggled to earn a place in this community. This second describes this general pattern of humanity's growth.
From post-modern, dystopian beginnings, corporations led humanity to reach beyond Earth and colonize the solar system with unanticipated technological advances until humanity overthrew the corporations. Our post-modern society strained Earth's resources as our population grew. Trans-national mega-corporations led humanity out of its dystopia through colonization of the Solar system. Luna, the asteroid belt and other key planetary moons were colonized first. Eventually, humanity domed parts of Mars and began a long-term terraforming project. Technological advances in subluminal propulsion, laser-burst communications and messenger boats helped keep humanity together. However, as humanity prepared to reach out into the stars, colonial revolt overthrew the patronizing corporations.
Humanity expanded beyond Sol under a Belter-Socialist government; establishing colonies who lost touch with their home. The Emergence Era ended after the Belter revolution established he Belter-Socialist terran government. Scientists discovered superluminal travel, which allowed humanity to establish colonies in hospitable systems. Travel hazards and times combined with local issues to lead colonies to break with Terran government and establish their independence.
During the First Decline, mankind is splintered on hundreds of worlds among dozens of starsystems. The HyperspaceVortices prevent FTL interstellar travel, and the interstellar economy collapses.
Humanity crept out of the First Decline as a renewed age of interstellar travel lead first from the ideal of interplanetary democracy through the autocracy of the Imperium before finally collapsing under the weight of a vast, corrupt bureaucracy and genocide.
The Imperium collapse ushered a dark period of violence and cultural darkness that ended when hop travel returned to reliability.
After nearly twelve centuries of chaos and war following the collapse of the Imperium, a number of wealthier interstellar states were united under a republican government. This Reunification began a peaceful and idealistic period of expansion. While sometimes tumultuous, all branches of humanity were finally united under one enlightened government.
With the establishment of the new, enlightened Reunification republic, humanity again began exploring interstellar space. The early impetus for this was to rediscover worlds lost during the Second Decline, and not necessarily to explore new systems. Still, with the unreliability of the charts and encyclopedic information that was left to them after twelve centuries, the two goals became intertwined.
However, this is not necessarily a good thing, because the other race was holding back on us. We eventually start meeting other races, warp technology freeing up the earlier jump limitations. But, humans were sort of behind the power curve and aren't the kings of the hill.
And, if you're not at the top, sooner or later you'll be under somebody's boot. Perhaps race in First Contact was looking for a good excuse to play master to our slave. Either way, humans are subjected en masse.
Fortunately, we are resilient, free-spirited, and the other race became a tad too complacent. We throw off our shackles and assert our equal role among the other races. This takes a while since having been dominated, it takes a while for everybody else to accept that we are a serious force to be accepted.