The majority of these planets were settled between 2310, which marked the launch of the first extra-solar colony ship, and 2490, when Reach became the UNSC's military center. As the UNSC began settling the Outer Colonies, the Inner Colonies, with their established social and economic infrastructures, became the political and economic basis of the UNSC, supplies with raw materials from the newer settlements.
Numerous ships were pulled from their positions in the Outer Colonies to defend the Inner Colonies. Old ships, such as the Halcyon-class Cruiser UNSC Pillar of Autumn, were refitted and brought back into service to supplement the remaining defense forces.
At the beginning of the Battle of Reach, dozens of Inner Colony planets were bypassed by the Covenant Fleet attacking Reach, so it can be presumed that a number of those Colonies survived, considering the next Covenant attack was Earth.
It is known that there was a war some time before the 26th century called the "Inner Colony Wars". Very little is known about it and it might just be an alternate name of the Interplanetary Wars, though the name would be of a post-Outer Colonies age, and probably only referring to the Sol system colonies.
Skopje - Glassed by The Covenant in 2547