If an opponent conquered a battlefield and then moved all units away, is it still considered an enemy conquered battlefield before I move my unit there?

Ruling: No, an empty battlefield is not considered conquered. A player loses control of a battlefield when they move all their units away from it.

Nuances:

• A card requiring "an enemy contested battlefield" would not be usable on an empty battlefield, even if the opponent previously held it
• When a player enters an empty battlefield that they don't hold, they will score a point for contesting it