When conquering an unoccupied battlefield, is there a showdown and are attacker/defender determined?

Ruling: There is a showdown for responses by players, but it is not a combat, so no attacker/defender is determined and no combat-related triggers or passive effects (like assault or attacking/defending triggers) occur.

Nuances:

• Effects that trigger on "showdown" will trigger
• Effects that trigger on "combat" or "attacking/defending" will not trigger
• Combat passive effects like assault do not apply
• Players can still play responses during the showdown (e.g., Hextech Ray)