In the eighteenth century, Spain, France, England, and the fledgling United States competed for control of North America, and after forty years of wars, treaties, territorial purchases, and the establishment of trading posts, the future of the United States became clear as the new nation pursued a continental domain. In the 1840s, leaders and politicians justified expansion to the Pacific as America's Manifest Destiny, while exploration by Lewis and Clark's Corps of Discovery from St. Louis to the headwaters of the Missouri River and beyond opened new knowledge at the dawn of the nineteenth century. After overland expeditions by trappers and explorers, the first wagon companies for California and Oregon set out along the Platte River in 1841 and 1843, Mormon pioneers bound for the Great Salt Lake followed in 1847, the Pony Express carried mail overland in 1860 just before completion of the transcontinental telegraph system, and by 1890 nearly 500,000 people had moved into the vast American wilderness. In five decades, California, Oregon, Kansas, Nevada, Nebraska, Colorado, North Dakota, South Dakota, Montana, Washington, Idaho, and Wyoming were granted statehood, and the fifty-year drama that populated those states with great-grandchildren of the colonists gave an abiding sense of romance to lands known simply as the West.