Does a battlefield conquer only occur if there are enemy units at the battlefield?

Ruling: A conquer occurs whenever Control of a battlefield changes, which can happen from player-to-player or from no one to a player. It is not required that enemy units were present.

Sequence:

• The battlefield is conquered if no defending units remain but attacking units do remain
• This results in an exchange of Control of the battlefield
• The exchange of Control causes a conquer

Nuances:

• Control can change from player-to-player or from no one to a player, and either counts as a conquer
• A battlefield can be controlled by a specific player or controlled by no one