The Mexican War began in 1846 with the breakdown in negotiations over a deal for the purchase of the disputed New Mexico Territory. U.S. troops went in to occupy the territory in dispute. A battle ensued at Palo Alto. The United States then declared war on Mexico and annexed the New Mexico Territory.
By 1847, the United States had captured and occupied Mexico City. A peace treaty finally was accepted by all sides on May 30, 1848.
At the outbreak of the war, the United States military forces were very small in number. There was a massive effort to recruit volunteers. Ultimately, 116,000 Americans served in the Mexican war. The majority of these were volunteers. A total of approximately 13,000 died, most of these from disease. The last U.S. troops left Mexico City on June 12, 1848.
If one of your ancestors was born between 1796 and 1830, they might be worth looking to see if they were involved in this war.
Mexican War
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Otis A. Singletary / Paperback / Published 1962
<a href="http://www.amazon.com/exec/obidos/ISBN=081602393X/northcarolingeneA/">The Mexican War (America at War Series)
Bronwyn Mills, John Bowman (Editor) / Hardcover / Published 1992
The Mexican War, 1846-1848
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K. Jack Bauer / Paperback / Published 1992
Mexican-American War 1846-48 (Brassey's History of Uniforms Series)
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Ron Field, Richard Hook (Illustrator) / Hardcover / Published 1997
The Mexican-American War, 1846-1848 (Men-At-Arms Series) Vol 56
Philip R. Katcher / Paperback / Published 1989
<a href="http://www.amazon.com/exec/obidos/ISBN=0306803496/northcarolingeneA/">The Story of the Mexican War
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Robert Selph Henry / Paperback / Published 1989