Pecos National Historical Park represents thousands of years of history that invites contemplation about where civilization comes from and how it further developed. The Developmental Period of the Pecos Valley was the introduction of early hunters and gatherers to the area where they took advantage of the wetter climate and agricultural benefits. By the mid-1100s, the Pecos Valley people began to live above ground in pueblos, or villages. It is during the Coalition Period when the population began to grow and the Upper Pueblo Valley villages were established. Since the Pecos Valley is located in New Mexico, the region became a U.S territory during the Mexican-American War in 1946. Towards the end of the 19th century, the valley became a central, transportation hub where trains and eventually cars travelled through. The mission of the historical park is to preserve the Indian pueblos and Pecos cultural remains. Pecos National Historical Park contains 12,000 years of history along with two Spanish Colonial Missions, Santa Fe Trial sites, and the site of the Civil War Battle of Glorieta Pass.