Enter ally if any. Units in an area may be ordered to move to any other area. Blitz may be ordered. Non allied units in the same area may remain ther but write as a move and treat as such when resolving orders. A move to an enemy area is always an attack.
Allied moves support the appropriate side, any others support defence.
Carry out retreats and land planes. At the end of a battle if attacking powers have a surface unit in the area then ownership belongs to the power which has the highest cost in the area, if defenders have surface units in the area then there is no change of ownership. Retreated units will defend the area to which they retreated if this is later attacked. Any units which are unable to retreat are lost without combat. New naval units may be placed in enemy occupied sea zone adjacent to an industrial complex.