Living Rules Reference · v2.0
5
Active System
The active system is the system that is activated during a tactical action.
When a player performs a tactical action, they activate a system by placing a command token from their tactic pool in that system. That system is the active system.
A player cannot activate a system that already contains one of their command tokens.
A player can activate a system that contains command tokens that match other players’ factions.
A system remains the active system for the duration of the tactical action during which it was activated.
Source: Twilight Imperium: Fourth Edition — Living Rules Reference v2.0 (September 22, 2020), page 9. Rules text reproduced verbatim; the rulebook’s diagrams are omitted.