On April 25, 1846, the United States declared war on Mexico and thus began one of the most dramatic and painful chapters in history. Due to the North American expansionist policy, and the resistance of the Mexican government to sell the northern states, an armed intervention of more than 10,000 soldiers was carried out, who faced a powerful Mexican army. The war extended to Mexico City and, in 1847, peace was agreed upon through the Treaties of Guadalupe-Hidalgo, in exchange for ceding several states in northern Mexico to the United States.