Once the player takes a solar system, the enemy breaks up the blockade to protect the solar systems.

Then combat against a defensive enemy (Objective 3).

If the player goes head to head at the blockade, they will lose, but if they maneuver through the asteroid belts thin points and take a little damage, they can conquer the less protected solar systems (Side Objective Flank).

Designers can set multiple goals with priorities, and the enemies will move to the highest priority threat with the higher total enemy.
A designer can also set an enemy to an aggressive, in which they prioritize goals, but then move toward any other opponent.
Without goals the enemy rely on sight.