Do 'When I Attack' triggers activate when moving to an uncontrolled battlefield?

Ruling: 'When I Attack' triggers activate when a unit is designated as an attacker, which typically happens when moving to a battlefield controlled by your opponent where a combat showdown starts. They do not trigger when moving to an uncontrolled/unoccupied battlefield.

Nuances:

• The trigger occurs when moving to an occupied battlefield (one with enemy units), not just any controlled battlefield
• In rare cases, a unit can become an attacker even if the opponent doesn't control the battlefield at the moment of attack
• If an enemy unit is removed during combat, units moved there still become attackers and triggers still activate (because the unit was present when combat started)