The New Colonial Alliance (or as the NCA) are an insurrectionist group first (as known) encountered by the 5th Marine Expeditionary Unit in 2557 after the 5th's 2 year status as MIA.
The NCA first formed prior to January 2553 by UNSC admiral Mattius Drake. The first attack made by the NCA towards the UNSC as a whole occurred when a group lead by rogue-Spartan Ilsa Zane attacked (the then top-secret) UNSC Infinity. However the first known engagement with the 5th occurred in 2557 when the 5th was sent to investigate Insurrectionist activity which resulted in the capture of the captain in charge. However the captain later escaped due to assistance of the defected Isabella O'Keth to the shock of much of the 5th.
- Due to the leaving of the member that plays O'Keth, it is unknown if the storyline relating to the character will continue.
- It is the first known singular hostile faction encountered by the 5th to have first appeared in the official Halo canon.