By the middle of the nineteenth century the United States had fulfilled the “manifest destiny” called for by so many expansionist newspaper editors and politicians. The Mexican War (1846–1848) brought more than 500,000 square miles of territory under the aegis of the country. The year 1850 saw California enter the Union as a free state, and other Pacific-coast territories soon followed suit. Within twenty years the country had constructed rail links, in the form of a transcontinental railroad, that bound the Atlantic and Pacific coasts together. With those acquisitions it seemed—to some—that the country’s territorial growth was complete.