The origin of the Mexican-
American War lies with Texas' 
request for admittance to the 
United States.  Despite Mexico's
threat of war, Texas was admitted
to the Union on December 29, 
1845, citing America's Manifest 
Destiny - the "right... to 
spread over this whole 
continent."  The US was well 
aware of mounting French, 
British, and even Russian 
interest in California, still a 
Mexican territory.  

Citing unanswered claims of US 
citizens against the Mexican 
government for injuries and 
property damage caused by 
Mexican nationals, General 
Zachary Taylor was sent with 
3,500 troops to make a show of 
force.  Camp Texas was 
established on March 24, 1846, 
across from the Mexican town of 
Matamoros, where some 5,700 
Mexican troops were already 
deployed.  On May 1, Mexico 
sent General Arista to siege 
Camp Texas. 

Taylor hurried back from Pt.
Isabel where he had been 
fortifying a second base.  On 
May 3, Taylor and 2,200 US 
troops engaged 4,500 Mexican 
troops on open ground at the 
Battle of Palo Alto.  The 
American artillery inflicted 
severe casualties on the Mexican
army; shaken, it fled as the US 
advanced onto Mexican soil.  The
following day at the Battle of 
Resaca de la Palma the US routed
the remainder of Arista's army. 
In just two days Mexico had 
suffered 1,100 casualties - the 
Americans suffered only 170.  
Four days later, the US 
officially declared war on 
Mexico.

At the outset of the war, 
General Taylor was ready to 
continue immediately following 
his stunning victory at Palo 
Alto and Resaca de la Palma.  
Due to the lack of supplies and 
logistical support, however, 
mobilization was slow.  The US 
army had been in a period of 
downsizing following the War of 
1812 (in August of 1842, 
Congress mandated a reduction 
in armed forces as an economy 
measure); as a result, the US 
would be vastly outnumbered in 
every battle of the war.  It 
was not until August that he was
able to continue into Mexico 
taking some 6,000 troops with 
him.

Taylor's advanced south to 
Monterrey; Colonel Kearny was 
ordered to occupy New Mexico and
California in the west; the US 
navy was ordered to blockade 
both Mexican coasts.

Taylor captured Monterrey on 
September 24 after three days of
spirited fighting.  On February 
23, 1847, Taylor defeated 
Mexico's General Santa Anna at 
Buena Vista, effectively ending 
Mexican resistance in Northern 
Mexico.  Meanwhile, California 
had declared its independence 
from Mexico and requested 
territoryship of  the US in 
July of 1846.  As Kearny marched
unopposed through the desert 
Southwest, the California 
question was closed.

In spite of these victories and 
the overwhelming success of the 
naval blockades, Mexico refused 
to give up.  Accordingly the US 
decided the only way to end the 
war was to occupy Mexico City.  
General Scott advanced and took 
Vera Cruz on March 29, 1847; 
without serious opposition, the 
summer saw victories through 
Cerro Gordo, Contreras, 
Churubusco, Casa Mata, Molino 
del Rey, and Chapultepec, the 
key to Mexico City.  Finally on 
September 14, Mexico City was 
captured and the war was over.

On February 2, 1848, a peace 
treaty was signed.  The Rio 
Grande was designated as the 
southern border of the US, with 
California and New Mexico being 
ceded.  As compensation, the US 
agreed to pay Mexico $15,000,000.
The US annexed only a portion of
Mexico due to many of the same 
reasons that led to the War 
Between the States.  While the 
South pushed for complete 
annexation, the North balked at 
the idea due largely to the 
looming debate of whether the 
new territory would be free or 
slave.  In addition, urban 
centers in the US were already 
straining under the influx of 
immigrants from Europe, with 
anti-foreign riots throughout 
the country - complete 
annexation of Mexico could 
start a wave of domestic 
problems.

The true impact of the Mexican-
American War was the power of 
the modern first used in the 
conflict. Throughout the war,
the American army went unbeaten.
Whereas the Mexicans were 
primarily armed with muskets, 
the outnumbered Americans relied
on the weapon that changed the 
face of warfare - the rifle.