system
Given the following post, respond as if you're commenting on Reddit:
human
[Halo] Did the UNSC have any reason to suspect a hostile alien force before first contact?

It's been a while since I read the novels, so my memory is a little fuzzy. I ask because it seems like earth and the major colonies had MAC stations in orbit around the planets before contact with the Covenant. I understand UNSC had been in a long standing war with the Insurrectionists, but as far as I remember they didn't have too much of a threatening fleet. What need did the UNSC have for so many orbital MAC stations? I can understand why the fleet was so large, they had a decent chunk of galaxy to patrol.
gpt
Yes. They were already aware of Forerunner facilities, and had been researching the few artifacts they had dug up. Some of the spookier factions of the UNSC pushed for more military hardware because they were expecting first contact with a technologically superior species like the Forerunners (and they were half right).

There was also some indications that frontier colonies were trading with Covenant merchant ships. ONI desperately wanted to cover that one up because of the Covenant's policy on client races, which would have sparked an all-out revolt before anyone would have figured out the Covenant would exterminate humans rather than bring them into the fold.