This is the 4475th most frequent Russian word.
восстанавливать
To restore or to recover.
The word 'восстанавливать' is used in the sense of bringing back to a former state (peace in this case).
Я стараюсь восстанавливать мир в семье.
I try to restore peace in the family.
Here, 'восстанавливать' refers to replenishing or regaining something (strength).
После тренировки нужно восстанавливать силы.
After training, it is necessary to recover strength.
In this context, 'восстанавливать' means to repair or reconstruct something to its previous condition (the castle).