LORE: "We're in attack position now, sir." "Hold here....We only need to keep them from escaping."
Place on a planet system if you occupy with at least a two Star Destroyers or Executor here or at Death Star orbiting this system. As long as your total Imperial starships outnumber opponent's, his starships may not move away. Also when you use Imperial Domination, opponent may not activate Force at related sites as well.