Maybe I'm off target with this since I've only been into BGS for a few months, but I've participated in forcing a faction to retreat by:
Adding inf++ to cause other factions to enter conflict/election/war to keep them out of the running thus blocking upward inf++ progress for the faction you want to suppress.
Add inf++ to all factions not in conflict and obviously not the faction you want to suppress by doing any quick to complete stacks of missions on the board and passenger lounge offering good inf++. I built a fast 800+ms boost iCourier to do stacks of simple data courier missions and collecting diplomatic bags/black boxes/hostage rescues/ planet surface station scans for this.
Adding inf++ to everyone except the faction you want to suppress seems to be very effective, although I'm not alone in doing this in fairly low population low traffic systems when I've seen it succeed against opposing player faction trying to take over a system. I've done it a lot in other systems too.
Adding inf++ to cause other factions to enter conflict/election/war to keep them out of the running thus blocking upward inf++ progress for the faction you want to suppress.
Add inf++ to all factions not in conflict and obviously not the faction you want to suppress by doing any quick to complete stacks of missions on the board and passenger lounge offering good inf++. I built a fast 800+ms boost iCourier to do stacks of simple data courier missions and collecting diplomatic bags/black boxes/hostage rescues/ planet surface station scans for this.
Adding inf++ to everyone except the faction you want to suppress seems to be very effective, although I'm not alone in doing this in fairly low population low traffic systems when I've seen it succeed against opposing player faction trying to take over a system. I've done it a lot in other systems too.