Each world is described by a system tile, placed in that hex during setup. Systems with a value of 0 are empty systems. Combat technologies - the space and ground technologies of any defending forces. Neutral Forces - the fleets and armies defending that system. Empty systems have no defending forces.
Space combat occurs after jumping a fleet into a system with unfriendly fleets.
Ground combat occurs when invading an unfriendly system. A combat is fought in rounds, until one side is destroyed or, in space only, retreats. In space, each Shield will absorb one hit per round. Thus, it takes four hits to do any damage at all to a fleet with three Shields. Owners assign losses and, in space, check cargo capacity before beginning the next round of combat.