:I don't see a POV problem here.  Saying "United States defeat" would be a redundancy because it's an undisputed fact that the U.S. lost the battle.  Describing it as a defeat makes no assertion or judgement about the moral value of the battle; it's just a plain fact.  The use of the word here is more of a context issue: the inquiries in question were conducted by the U.S., so it's only natural to speak of them in terms that reflect what they were studying.  If we were talking about Indian accounts of the battle instead, then it would be correct to refer to it as a victory in that context.