Date of war: (1846-1848)  

Population: 21,100,000

Service Members: 78,718

Ratio: 0.4%

Casualties: 13,283 Dead, 4,152 Wounded

Financial Cost in billions (1990s): $1.1

The Mexican-American War (1846-1848) denoted the main U.S. furnished clash essentially battled on unfamiliar soil. It pitted a politically separated and militarily ill-equipped Mexico against the expansionist-disapproved organization of the U.S. President James K. Polk, who accepted the United States, had a "show of predetermination" to spread across the mainland to the Pacific Ocean. A line clash along the Rio Grande got the battling going and was trailed by a progression of U.S. triumphs. At the point when the residue cleared, Mexico had lost around 33% of its region, including virtually all of present-day California, Utah, Nevada, Arizona and New Mexico

Causes 

Texas gained its independence from Mexico in 1836. Initially, the United States declined to incorporate it into the union, largely because northern political interests were against the addition of a new slave state. The Mexican government was also encouraging border raids and warning that any attempt at annexation would lead to war.Nonetheless, annexation procedures were quickly initiated after the 1844 election of Polk, who campaigned that Texas should be “re-annexed” and that the Oregon Territory should be “re-occupied.” Polk also had his eyes on California, New Mexico and the rest of what is today the U.S. Southwest. When his offer to purchase those lands was rejected, he instigated a fight by moving troops into a disputed zone between the Rio Grande and Nueces River that both countries had previously recognized as part of the Mexican state of Coahuila.On April 25, 1846, Mexican cavalry attacked a group of U.S. soldiers in the disputed zone under the command of General Zachary Taylor, killing about a dozen. They then laid siege to an American fort along the Rio Grande. Taylor called in reinforcements, and–with the help of superior rifles and artillery–was able to defeat the Mexicans at the battles of Palo Alto and Resaca de la Palma.

Following those battles, Polk told the U.S. Congress that the “cup of forbearance had been exhausted, even before Mexico passed the boundary of the United States, invaded our territory, and shed American blood upon American soil.” Two days later, on May 13, Congress declared war, despite opposition from some northern lawmakers. No official declaration of war ever came from Mexico.

End of the War  

Guerilla assaults against U.S. supply lines proceeded, however in every way that really matters, the conflict had finished. St Nick Anna surrendered, and the United States sat tight for another administration equipped for arrangements to shape. At long last, on Feb. 2, 1848, the Treaty of Guadalupe Hidalgo was marked, setting up the Rio Grande and not the Nueces River as the U.S.- Mexican line. Under the deal, Mexico likewise perceived the U.S. extension of Texas, and consented to sell California and the remainder of its region north of the Rio Grande for $15 million or more the presumption of specific harms claims.