Capture systems (Stellaris)

Good evening,
I just recently started playing this game.
The question is: EDN war faction took control of the system, and destroyed the Outpost. System as an Outpost, my but they are in enemy territory, and in the menu of the Outpost says that it can't strengthen as it occupied(???)

How to make that she would become fully mine. I have a system predyavlyal of problem in the beginning of the war