The Mexican-American War was an armed conflict between the United States and Mexico which lasted for two years—from April 1846 to February 1848. One of the main causes for the war was the United States' annexation of the Republic of Texas in 1845, which gained independence from the Republic of Mexico in 1836. The Americans and the Mexicans argued over the southern and western borders of Texas, as Mexico claimed that Texas ended at the Nueces River, while the US claimed that it ended at the Rio Grande river.

The number of Americans who died in the war is a bit over 13,200, while the Mexican government estimates that as many as 25,000 Mexicans (both soldiers and civilians) died during the Mexican-American War. It's notable to mention that many of those who lost their lives in the war died from disease, poor conditions, and lack of hygiene; in fact, some historians even argue that only 1,190 Americans died in combat, more than 800 died from their wounds or accidentally, and more than 11,000 died from disease.

The exact number of Mexican deaths remains a mystery to this very day, with some placing the figure at around 9,000 (5,000 soldiers and 4,000 civilians). The number of wounded people was also high on both sides, with over 4,000 wounded Americans and thousands of wounded Mexicans.

In the end, the United States won the war, and actually they never lost a battle, mainly due to Mexico's weak political and socioeconomic climate, as well as their military unpreparedness. As a result, Mexico had to give up a lot of its territory and gained only 15 million dollars in return.