Question: The wording of the [Bred for War](http://www.d20pfsrd.com/traits/race-traits/bred-for-war) trait is as follows:

> 
> **Bred for War**
> 
> 
> You tower above most other humans and possess a physique of hard,
>  corded muscle.
> 
> 
> Benefit You gain a +1 trait bonus on Intimidate checks and a +1 trait
>  bonus on your CMB because of your great size. **You must be at least 6**
> **feet tall.** (Emphasis Mine)
> 
> 
> 

Someone on the Pathfinder Society Facebook Group stated they have a Halfling who is 8 feet tall because they used the [Adopted](http://www.d20pfsrd.com/traits/social-traits/adopted) Social Trait to select it. I read the trait as *requiring* you to be six feet or taller to select the trait, not permitting an otherwise Small race to become taller than six feet via its selection.

Answer: 
You could use the Bred for War racial trait as a member of an adopted species, but that wouldn't give you any sort of benefit if you're less than six feet tall. The Bonus to intimidate is a result of you being unquestionably large. 

If you're a halfling adopted by half-orcs you will never be as intimidating as they are because you lack the physical stature the racial trait requires to attain its effect.

By the same token, a Human could use Adopted to get bred for War and be just fine provided they were at least six feet tall. In a way the "six feet tall" requirement is a prerequisite, even if it doesn't seem to be listed as such.
The wording is quite lear there. "You must be at least 6 feet tall." means exactly as it is stated. For this trait to work or have any effect you must be at least this "points finger at the 6 feet line" tall. 

I would take it as an oversight that it is not put into a separate required part of the document (there are only very few such oversights for such a large number of traits,...). 

So if the halfling is somehow over 6 feet tall (or just 6 feet) he can use it by all means (and adopted trait). Else no.