Take humanity's first faltering steps out into the wider galaxy in Galactic Civilizations 3's Rise of the Terrans DLC, which takes you back to the formative days of Earth's Terran Alliance. It's a new prequel campaign for the strategy game, and you can buy it now for the price of $4.99/£3.99, from Steam or Stardock, or maybe by flinging a couple of coins into a wishing well. I haven't tested that method, but you never know. Developer Stardock has this to say about the DLC:
"Destiny might be calling, but you are not alone and will soon discover that not every race is welcoming. Your choices will guide your people’s future as you face down new and unexpected threats, build your empire, and explore the furthest corners of space."
To be fair, you could use that description for the main game, or for any space-based 4X, really. You'll play as a new faction in this campaign, a faction featuring a new trait that "boosts experience gained from ship battles with the United Earth faction". Which is nice. (Ta, Blue's News.)