States, while the war of conquest advanced further to the West. In the end of September Kearny started out from Santa Fé for California, where he arrived early in the following January. The conquest of the Southwest extended the boundary of the United States to the Gila and the Pacific, broadening the area of the desert within the United States and raising new problems of long-distance government in connection with the populations of New Mexico and California. The Santa Fé trail, with its continuance west of the Rio Grande, became the attenuated bond between the East and the West. From the Missouri frontier to California the way was through the desert and the Indian Country, with regular settlements in only one region along the route. The reluctance of foreign customs officers to permit trade disappeared with the conquest, so that the traffic with the Southwest and California boomed during the fifties. The volume of the traffic expanded to proportions which had never been dreamed of before the conquest. Kearny's baggage-trains started a new era in plains freighting. The armies had continuously to be supplied. Regular communication had to be maintained for the new Southwest. But the freighting was no longer the adventurous pioneering of the Santa Fé traders. It became a matter of business, running smoothly along familiar channels. It ceased to have to do with the extension of geographic knowledge and came to have significance chiefly in connection with the organization of overland commerce. Between the Mexican and Civil wars was its new period of life. Finally, in the seventies, it gradually receded into history as the tentacles of the continental railway system advanced into the desert. The Santa Fé trail was the first beaten path thrust in advance of the western frontier. Even to-day its course may be followed by the wheel ruts for much of the distance from the bend of the Missouri to Santa Fé. Crossing the desert, it left civilized life behind it at the start, not touching it again until the end was reached. For nearly fifty years after the trade began, this character of the desert remained substantially unchanged. Agricultural settlement, which had rushed west along the Ohio and Missouri, stopped at the bend, and though the trail continued, settlement would not follow it. The Indian country and the American desert remained intact, while the Santa Fé trail, in advance of settlement, pointed the way of manifest destiny, as no one of the eastern trails had ever done. When the new states grew up on the Pacific, the desert became as an ocean traversed only by the prairie schooners in their beaten paths. Islands of settlement served but to accentuate the unpopulated condition of the Rocky Mountain West.