Prior to the start of the war with the Covenant, humanity had established colonies on around 800 separate worlds. Most human colonies were small, populated by well under one million people, while a few were very large, with a population in the hundreds of millions.
There is not much known about the populated world of the Covenant and the Covenant species. That which is known is due to the work of the Office of Naval Intelligence.
Though the Forerunners disappeared over 100,000 years ago, their legacy lives on in the form of their massive constructs.
ANCIENT HUMAN WORLDS
Before human civilization as we know even existed, ancient humanity was travelling the stars and building a galactic empire.