In the eighteenth century, Spain, France, England, and the fledgling United States competed for control of North America, where command of rivers, seaports, forests, rich soils, and wildlife resources was vital to building a strong, stable empire. American settlement and governance aimed to secure the trans-Mississippi West against rival nations. During the first half of the nineteenth century, trappers, explorers, Oregon settlers, Mormon pioneers, and California gold seekers created a network of trails leading west from the Mississippi River. By 1860, the Pony Express used existing stagecoach routes and stations between Missouri and California to sustain rapid overland communication between west and east. In roughly fifty years, the frontier moved from the Mississippi River valley to the Pacific Ocean, and this trail served as a conduit for westward expansion as emigrants passed through Wyoming on foot, driven by dreams of helping shape the future of their continental nation.