The form of western riding generated from the cowboys that rode on their ranches out west. A western saddle is different from the English saddles because it has a horn. A western saddle purpose was to help the rancher out when he was doing his daily chores.
Western is branched off into performances disciplines such as reining, barrels, poles, and western riding. These events take speed and agility but are performed in western attire.
Western is also mostly thought of the relaxing disciplines like western pleasure and trail. These events require smooth gaits and should show how you horse is a pleasure to ride. Also in trail the horse is to move through obstacles with ease and patience.
Western Horsemanship focuses on the rider's capability to control and ride their horse. You are scored on your riding skills as well. Most of the time you perform a pattern with your horse.
Here are some links if your interested in learning more about these disciplines:
Equiworld