One of the first consequences for Mexico meant living next to a much more productive and more powerful country in the process of economic and territorial expansion was the loss of about 50% of its area. The great sacrificed with the “conquest of the West” was Mexico, which in the first half of the nineteenth century did not have the adequate resources to adequately protect the vast semi-populated areas of the North that since the beginning of the century were subject to aggressive colonization by American farmers, ranchers, merchants and adventurers. In the sight of these appeared in first place Texas, a vast and rich territory equivalent to more than half of the surface of Colombia.
As early as 1829, President Jackson proposed to the Mexican government the purchase of Texas with the following arguments: “The comparatively small value for Mexico of the territory in question; its remote and disconnected situation; the disarranged condition of their businesses; the repressed and languishing state of its finances … everything contributes to pointing out and recommending to Mexico that which detaches itself from a portion of its territory that is of insufficient and problematic benefit”.
After several years of clashes with the troops of the Santa Anna regime, the American residents proclaimed the independence of Texas in March 1836. The subsequent entry of Texas into the American Union (July 1845) and the numerous border incidents between Mexican forces and Americans, made the open war between the two nations inevitable, which lasted between 1846 and 1848.