From the Annals of Unjust Wars –  In 1848, the United States and Mexico signed the Treaty of Guadalupe Hidalgo ending the Mexican-American war – the last time the U.S. fought with one of its neighbors. The Treaty was a humiliating defeat for Mexico stripping it of approximately 1/3 of its territory and adding that 525,000 square miles to United States territory.  The new territory comprised California, Nevada, Utah, New Mexico, Arizona as well as parts of Texas, Colorado and Wyoming.  The war had been launched over controversy regarding the border between Texas and Mexico.  The U.S. claimed the Rio Grande while Mexico claimed the Nueces River as the boundary.

The last act of President John Tyler before leaving office in 1845 had been to annex the Republic of Texas. Incoming President James Polk had greater designs on the west.  Polk did attempt to buy land from Mexico, but his emissary John Slidell was stonewalled by the Mexican government.  Rebuffed, Polk sent American troops to the disputed border region in Texas in January of 1846 to provoke the Mexicans into war. When the Mexicans fired on American troops in April of 1846, Polk had the excuse he needed. He declared, “[Mexico] has invaded our territory and shed American blood upon American soil,” and sent the order for war to Congress on May 11.

Polk’s motives were likely mixed.  He had run for President in 1844 on a Democratic platform that supported manifest destiny, but many Northerners believed that Polk was trying to gain land for the slaveholding South.  Others opposed the war on the grounds that it was a war of territorial conquest.  Ulysses S. Grant, who fought in the war with many others who would be come famous in the U.S. Civil War, called the war “one of the most unjust ever waged by a stronger against a weaker nation. It was an instance of a republic following the bad example of European monarchies, in not considering justice in their desire to acquire additional territory.”  The newly acquired territory certainly helped lead the U.S. into more controversy over the expansion of slavery as the U.S. slid inexorably into civil war only 13 years later.