There are two different kinds of "war bridles". The original war bridle is a piece of riding equipment used by native Americans. The cowboy version of a "war bridle" is a sort of halter used on disrespectful horses. This article is about the use of a native american War Bridle. A war bridle CAN be harsh in the wrong hands but used by a careful rider who rides mostly off their seat and legs it is a very gentle form of control. If you can't stop your horse without using your reins, you aren't ready for a war bridle.
The indian war bridle is made from a single piece of rope. It loops through the mouth where the bit would sit, ties around the jaw in a type of slip knot, then runs back as reins.
The way this bridle is MEANT to be used is very subtly, if at all. Because of the single knot under the horse's jaw, it's very difficult to turn a horse using the reins of a war bridle (and would be painful or at the very least uncomfortable if you tried!) turning has to be initiated by the rider's body and legs.
It's a neat piece of tack for an advanced horse, or for an advanced rider who wants to train a horse in native american style or break a horse who is for some reason unable to wear a headstall. But for the rest of us, a war bridle is a piece of tack that should be used only after a horse can stop, turn, and change gaits, bareback, with zero contact on the reins.