Rensa’s world was colonized as part of a wide spread defensive program by a heavily populated world that was itself a granddaughter colony of Earth. It sits in the Scutum-Centaurus arm of the Milky Way galaxy, the late-born daughter of a late born-daughter of the human home world. Through design and circumstance it lay far beyond any other successful human world. Then they found out that something was coming towards them.
Something big, something slow and that, because space is big, gave them time to come up with a plan and implement it.
Their strengths were their high population, their technologies and their planning. Their weaknesses were their reliance on plans made by people who would not have to implement them in places they had never been, failure to anticipate the ways human nature and the systems they had developed to implement their plans would interact, and attempts to reduce the costs of implementing their plans as they were rolled out. It is fair to say that if anything could go wrong with the plans and/or their implementation, then there is a world where it has.
Their plan was to seed a network of colony worlds in a barrier along and across the path the threat must take to get to them. The arrival of the threat in each location has been calculated and each colony’s development plan will have it ready to fight the threat when it arrives. The strategy is that each colony will be an independent firebase capable of denying an attacker the opportunity to obtain resources and succor from its solar system. The plan attempts to deliver survivability for the colonial populations but they are, essentially, expendable in the defence of the megapolis of the founding world and its core colonies. The plan is a war of attrition that will wear the threat down so that the home world can survive and withstand the expected onslaught.
This is not the sort of information the colonies teach in primary schools.