A common platform for armor that incorporated advanced sensors and drones for exceptional situational awareness. It incorporated new active defense systems such as countermeasures, soft and hard kill, but also ERA.
The idea of simple massive armor (only possible for a small area because of weight constraints) ended.
The idea was that you would have a common platform regarding powerplant, sprocket, tracks... Logistics is easier.
https://en.wikipedia.org/wiki/Future_Combat_Systems_Manned_Ground_Vehicles
Thank you for the clarification re FCS.