May 13: United States declares war on Mexico in 1846.

This painting (circa 1872) by John Gast  calledAmerican Progress, is an allegorical representation of the modernization of the new west. Here Columbia, a personification of the United States, leads civilization westward with American settlers, stringing telegraph wire as she sweeps west; she holds a school book as well. The different stages of economic activity of the pioneers are highlighted and, especially, the changing forms of transportation.

On May 13, 1846, the United States declared war on Mexico. The fighting lasted a year and a half. The Guadalupe-Hidalgo Treaty forced the sale of 3.1 million square kilometers (nearly three times the Colombian mainland). Mexico ceded territories of New Mexico and California which the US armies occupied immediately.

United States paid Mexico $ 15 million, and also assumed the Mexican debt to the private sector by $ 3.5 million (that is a total of $ 18.5 million over 3 million square kilometers!). 

Additionally, Mexico accepted the loss of Texas and agreed that the national boundary was the Rio Grande. In short, the United States took over half of the territory to Mexico.

The US territorial expansion to the Pacific was a goal of President James K. Polk who firmly believed the doctrine of Manifest Destiny of USA by which the American nation was destined to expand from the shores of the Atlantic Ocean to the Pacific Ocean, because God wanted it!

Like it or not!

Indeed, the belief was that it should expand also across the continent which led the US government to intervene in several countries in Latin America. Actually, the original belief or doctrine held that it was the destiny of the United States of America to expand its territory over the whole North America, only.