When it comes to the single biggest influence in shaping life in the Old West, it would be hard to get past that four-legged critter made famous in books and movies -- the horse.
Certainly, the railroad radically influenced settlement of the West when it came along, completion of coast-to-coast rail service, and completion of a coast-to-coast telegraph system both mightily influenced everything about westward expansion and settlement. But from beginning to end, the West relied in one way or another on horses. Early trappers and pioneers who expanded "Anglo" influence into every area we call the Old West, came on foot, came dragging and pushing various forms of sleds and sheds and wagons -- but they all came at one time or another riding and/or leading horses and horse drawn vehicles.
Indeed, the earliest settlements in the Old West were Spanish-Mexican-Indian settlements dependent largely upon the horse. In fact, most of the Native American cultures in the West were shaped or reshaped by the presence of horses.
Then, of course, there are the legendary images we all have thanks to television and movies of the cowboys and their faithful horses.
So from hauling wagons to plows, herding cattle to carrying soldiers, we applaud the horse. Without the horse, there would be no Old West. Or at least it would have looked and been very, very different.