The Inner Colony Wars were a series of conflicts that occurred sometime in human history. Very little is known about the wars, or if they were a distinct event at all. Of what is known, "instant, uninformative news reports caused massive civil unrest" and "almost tore down Earth's culture." 
The Inner Colony Wars have been referenced in the story Second Sunrise Over New Mombasa in the Halo Graphic Novel and in the Halo: Legends short Origins. Few details are given, and it may actually be an alternate name for the Interplanetary War and the other conflicts in the 2160's where the United Nations clashed with the Koslovic and Frieden forces in the Sol system, resulting in the formation of the United Nations Space Command and the Unified Earth Government. While the concept of the Inner colonies did not exist at that time, it is possible that the name "Inner Colony Wars" was coined after the formation of the Outer Colonies, as the story itself takes place in 2552.
Assuming that the Inner Colony Wars were a distinct event and that the name "Inner Colony Wars" has been in use since the war itself, they may have occurred in the 25th century as there obviously was no distinction between Inner and Outer colonies before the establishment of the Outer Colonies.
- Halo Graphic Novel (First appearance)