The Pegasus Expedition
The worldbuilding is mostly based around the Pegasus Galaxy and how humanity wants to exploit it. The premise is this: Humanity is getting torn apart by an aggressive alien race called the Colossals, so they sent three fleets to the Pegasus Galaxy to get some resources and reinforcements. These fleets consist of the Middle East, the US, and the EU (the EU is playable); the Chinese fleets are instead holding the line by Earth.
When humanity enters the Pegasus Galaxy, they get a very frosty reception. They appear in an organization’s territory who immediate try to push the humans back to their portal. The organization is instead wiped out by the humans, and the organization’s bosses - resembling the Roman Empire - tells humanity to back off or the Empire will kick them out.
There’s some politics stuff that happens in the Middle Eastern and US fleets later on, as well as a Flood/Thing-esque crisis that shows up. In the end, the EU gathers up all of its new friends in the Pegasus Galaxy to push through Flood/Thing turf and rescue the humans on Earth.
The gameplay is a bit dodgy but I think the worldbuilding and story are rock solid.
Another game with interesting worldbuilding is White or Black (by ZeroCreation).
In that one, humanity nearly destroyed itself after an incredibly devastating WW3. Therefore, to avoid the constant Cycling of Empires, a band of philosophers and religious people tried to make one final civilization that lasts forever, which completed its rise to world domination in the late 21st century. Some interesting tidbits about this final civilization: