 During the 16th century, Spain focused on conquering areas with dense populations that had produced Pre-Columbian civilizations.These populations were a disciplined labor force and a population to convert to Christianity.Territories populated by nomadic peoples were harder to conquer, and although the Spanish explored much of North America, seeking the fabled "El Dorado", they made no concerted effort to settle the northern desert regions in what is now the United States until the end of the 16th century (Santa Fe, 1598).