The Mexican period of the U.S. southwest lasted from 1821 until 1848. The First Mexican Republic (1824-1835) had difficulties maintaining control over the region. Sparsely populated and far from the economic and political center in Mexico City, the northern territories of Alta California, Santa Fe de Nuevo Mexico, and Tejas were now free to engage in economic exchange with American traders, a practice which had been barred under the Spanish Empire. This newfound freedom resulted in the development of strong economic and social ties between the economic elites of Tejas, Alta California, and the United States.