Does Yone's ability trigger when conquering a battlefield through surprise defense combat?

Ruling: Yone's ability triggers when you conquer an "open battlefield," which means an uncontrolled battlefield (not controlled by any player). This includes conquering through surprise defense combat, since the battlefield is uncontrolled when you conquer it.

Nuances:

• "Open battlefield" is not officially defined in the rules but is interpreted as an uncontrolled/empty battlefield
• If there were friendly units, there wouldn't be a showdown; if there were enemy units, there would be combat
• The battlefield must be uncontrolled at the time of conquest for Yone's ability to trigger