system
Given the following post, respond as if you're commenting on Reddit:
human
[Mass effect] How did humanity conquer space that fast?

During the events of mass effect 1, it's been mentioned that humanity made contact with aliens 26 years ago. Obviously it helps to establish people from before and after meeting aliens but there's some narrative problems. How much of a planet do you have to explore before you can say that you have conquered it? How did humanity take control of entire criminal organizations, syndicates, economies and advertising when the Volus who have been around far longer couldn't? 26 years just seems too short of a time for humans to make peace with aliens.
gpt
Humanity first made contact with aliens 26 years ago, but they'd already been an interstellar civilization for a long time prior to that.  Humans had discovered the Charon Relay near Pluto, and was using it to travel to other solar systems and establish colonies on other planets.  In fact, first contact with an alien species happened when a turian patrol came across a human ship activating a dormant mass relay, which was forbidden by the Citadel Council, because that's the kind of recklessness that led to the Rachni Wars.  So the turians destroyed the human ship, and then beseiged the nearby colony of Shanxi.  Then the humans sent more ships to liberate Shanxi, and both the humans and turians started preparing for all-out war, but the Council stepped in before things could get out of hand and brokered peace.  

As for why humans could expand so fast, that's basically what distinguishes humanity from other species in the Mass Effect universe.  Humans are ambitious, determined, and incredibly versatile.  Humanity's rapid expansion has surprised everyone, including all the other alien species and probably many humans themselves.