Mexican War 1846-1848
Causes of the Mexican War
 Manifest Destiny
 Annexation of Texas
 Slavery
 Economics
 Dispute over the Rio Grande Border
What is the controversy over Texas?
Texas Annexation
 Texas declared
their
independence in
1836, which
Mexico did not
recognize
Texas Annexation
 Texas asked Jackson and Van Buren to annex
them, they refused. Why?
 Tyler was leaving office in and he agreed.
Why?
 February 1845 Congress approved the Texas
Annexation
Problem of Texas
 The Republic of Texas hoped annexation
would solve the republic’s financial &
military problems
 Texas becomes the 28th state in December of
1845.
 Mexico reacts by cutting off all diplomatic
ties with the U.S.
Slavery was a key issue in the case of Texas
and the Mexican War
• Enforcement of Mexico’s law on slavery was a cause
of the Texas revolt
• Slavery was major issue in annexation debate
Other factors that were unrelated to slavery
• Ambition to acquire California—land and sea ports
• Gadsden Purchase—railroads
War Powers of the President
1827 Martin v Mott -
Constitutional for Congress to vest the president
with the discretionary authority to decide whether
an emergency has arisen and to raise a militia to
meet such a threat of invasion or civil insurrection.
Did such a threat exist in winter of 1845-46?
Boundary Dispute
 Texas and U.S. claim that the Rio Grande marks the
southern border of Texas
 Mexican government rejects this idea and argues
that the real southern border is the Nueces River
Rio Grande boundary
Nueces River boundary
Steps to War
 June 1845- President
Polk ordered General
Zachary Taylor to take
U.S. troops into
disputed border
region
 Polk claims this action
is to protect Texas
from possible Mexican
attack
Steps to War
 Meanwhile, Polk sent
diplomat John Slidell to
Mexico City to negotiate
the purchase California &
New Mexico for $30
million
 Mexican officials refused
to meet with Slidell
John Slidell
Steps to War
 March 1846 – General Taylor’s troops made camp at
the Rio Grande in disputed territory
 April 1846 – Mexican commander insisted U.S. troops
must leave area and Taylor refused to move
 Mexican forces crossed the Rio Grande and attacked a
group of 63 U.S. soldiers
 11 Americans killed
Steps to War
 May 11, 1846 – Polk addressed Congress
 He declared that “Mexico has shed American blood
upon the American soil.”
 Two days later Congress declared war on Mexico
War Votes:
House: 174-14 and Senate:40-2
Support of the War
 Many people who supported the war believed it would
spread republican values—what are they?
 Many southerners supported the war, thinking any
territory won would be organized into slave states
 For many Americans the war led to greater national
pride—thousands of young men rushed to volunteer
Support of the War
“Yes: Mexico must be thoroughly chastised!...Let our arms now be carried with a spirit
which shall teach the world that, we are not forward for a quarrel, America knows
how to crush, as well as how to expand!”-Walt Whitman
“The universal Yankee nation can regenerate and disenthrall the people of Mexico in a
few years; and we believe it is a part of our destiny to civilize that beautiful
country.”—NY Herald
“(The Mexicans are yielding) to a superior population, insensibly oozing into her
territories, changing her customs, and out living, out-trading, exterminating her
weaker blood.”—American Review
“Shall this garden of beauty (California) be suffered to lie dormant in its wild and useless
luxuriance?...myriads of enterprising Americans would flock to its rich and inviting
prairies; the hum of Anglo-American industry would be heard in its valleys;…and the
resources of wealth of the nation be increased in an incalculable degree.”—Illinois
State Register
Opposition to the War
 Many members of the Whig Party thought the
conflict was unjustified
 Northern abolitionists feared any territory gained in
the war might be organized into slave states
 Illinois Congressman Abraham Lincoln wrote the
“Spot Resolutions” in 1848– asking Polk to show the
spot where American blood had been shed on
American soil
Famous Opposition
 Tom Corwin of Ohio accused Polk of involving the US in a war
 of aggression.
 Daniel Webster: Doubts about the constitutionality of Polk’s
action, believed that Congress had not been adequately
consulted.
 Henry David Thoreau: refused to pay $1.00 poll tax because he
believed that the war was an immoral advancement of slavery.
 John Quincy Adams: described war as a southern expedition to
find “bigger pens to cram with slaves.”
 Charles Sumner: a noted abolitionist, also condemned the war
from pacifist principles.
Quote from a Freshman Representative
“If to say “the war was unnecessarily and
unconstitutionally commenced by the President” be
opposing to war, then the Whigs have very generally
opposed it. . . . The marching an army into the midst
of a peaceful Mexican settlement, frightening the
inhabitants away, leaving their growing crops and
other property to destruction, to you may appear a
perfectly amiable , peaceful, unprovoking procedure;
but does not appear so to us…..”
Abraham Lincoln, April 1846,
Speech in the House of Representatives
Mexican War
Polk sets precedent for Presidents in war
Three Theaters of the War
Northern Mexico
Gen. Zachary Taylor
Battle of Monterrey
Battle of Buena Vista
New Mexico- California
Col. Stephen Kearney
Gen. John C. Fremont
Bear Flag Republic-CA
Central Mexico
Gen. Winfield Scott
Battle of Vera Cruz
Battle of Mexico City
The Treaty of Guadalupe Hidalgo (1848)
 Mexico: 1) Gave up NM, CA and AR
2) Recognize the Rio Grande as the Border
 USA:
1) Pay Mexico $15 million
2) Pay all outstanding debt between
owed to Mexico--$3.5 Million
 Ends the war, but no one is really happy:
President Polk wanted more land, the Whigs
thought we took too much land.
The Results of the Mexican War
• Get
1 Million sq miles for $118.5 Mill
• 13,000 Americans killed (1,800 in battle,
11,200 from disease).
• Trained soldiers for the Civil War
How did the Mexican War start the nation
on the Road to the Civil War?
Issue of Slavery is raised again!
 Wilmot Proviso
---Beginning
in 1846 it stated that slavery
should not be allowed in any territory acquired
from Mexico.
--While it never passed, the Wilmot Proviso
provided a well-defined proposal that allowed
the free-soil forces to attract thousands of
followers.
Southern Manifest Destiny in the 1850’s
South wants to gain more land for slavery
• Ostend Manifesto-Cuba
• Walker Expedition-Nicaragua
• Clayton-Bulwer Treaty-Panama Canal
Review Questions
 What were the reasons for American Expansion?
 Who specifically was in favor of this? Opposed?
 What was controversial about the Texas annexation?
 What were the problem(s) between Texas and Mexico?
 How did Polk win the Election of 1844?
 What were his goals?
 What issues were involved with the Oregon Territory?
 What were the factors that led to the Mexican War?
 Who specifically was in favor of the war? Opposed?