Cause and Effect
The Mexican-American War
Objective : Determining the causes of the Mexican American War
U.S.-Mexico Disputes
• The Annexation of Texas by
the U.S. angered the Mexican
Government.
• Mexico never acknowledged
Texas as independent and felt
the U.S. had no right to take
its territory.
• Mexico also did not
acknowledge the Treaty of
Velasco which set the
southern border of Texas as
the Rio Grande.
• The loss of Texas will inevitably result in the
loss of New Mexico and the Californias. Little
by little our territory will be absorbed until
only an insignificant part is left to us.... Our
national existence... will end like those weak
meteors that, from time to time, shine fitfully
in the firmament (sky) and disappear.
-José Maria Tornel y Mendivil
The U.S. and Texas considered the Rio Grande as the
Southern border. For Mexico it was the Nueces
Area in Dispute
Nueces River
Rio Grande River
• Why would the Mexican government not
accept the treaty of Velasco?
– Santa Anna only signed the treaty of
Velasco because his life was in danger.
Manifest Destiny
• Another issue with Mexico was Manifest Destiny.
• The land that the United States desired out west
(California especially) was all controlled by Mexico.
The U.S. Perspective
• Most Americans sympathized
with Texas during the Texas
revolution and republic days
because most Texans were
former Americans.
• As a result of the brutal
fighting (at the Alamo,
Massacre at Goliad, and other
times) the American public
developed negative
stereotypes against the
Mexican people and
Stereotype: A belief that is incorrectly
government
attributed to an entire group of people
Effort to ease the tensions
• After Texas Annexation,
Mexico threatened war.
• U.S. President James K.
Polk sent John Slidell to
Mexico to work for better
relations between the
two countries.
John Slidell
Slidell’s Mission
1) Get Mexican recognition of the Rio Grande as
the border between Mexico and the United
States
2) To forgive about $4.5 million owed to U.S.
citizens by Mexico from the Mexican War of
Independence
3) To discuss the purchase of the New Mexico
and California
• The Mexican government refused to talk with
Slidell which angered the U.S.
• A company of U.S. Calvary
by Captain Seth
The Thornton Affair commanded
Thornton got into a skirmish with
Mexican forces near the Rio
Grande.
• Thornton was ordered to scout an
area about twenty miles northwest
of what later became Brownsville,
Texas. In April 1846, the Calvary,
investigated an abandoned
hacienda (Ranch).
• Some two thousand Mexican
soldiers were encamped in and
around the hacienda, and a
firefight occurred. Both sides
Thornton was outnumbered
fought ferociously, but the greatly
By about 1900 men.
outnumbered U.S. force was forced
to surrender after several hours of
Skirmish: A small battle
skirmishing.
Presidents Polk’s
Response
• President Polk asked for a declaration of war before a joint
session of the United States Congress, summing up the need
for war by famously stating:
– "American blood has been shed on American soil".
• Congress declared war on Mexico, despite protests by the
Mexican government that Thornton had crossed the border
into Mexican Texas — a border that Mexico claimed as the
Nueces River. the ensuing Mexican-American War was waged
from 1846-1848 and witnessed the loss of many thousands of
lives and nearly half of the territory of Mexico.
• US Problems with
Mexico
1) Americans had a
negative view of
Mexico because of
the Texas
Revolution
2) Mexico owed the
U.S. money for the
Mexican Revolution
against Spain
• Mexican Problems with
US.
1) Mexico felt that Texas
was being stolen from
them.
2) Mexico didn’t believe
in Manifest Destiny and
didn’t want to give
away their land.
Vote Yes-Declare War
• Treaty of Velasco is
valid
• Belief in Manifest
Destiny
• Texas Annexation is
legal
Vote no-not to Declare
War
• Will expand slavery
• Manifest Destiny is
unfair to Mexico
• Treaty of Velasco is a
sham and not valid
• Annexation is illegal
without Mexico
approval.
POLK’s Speech Video