Chapultec Castle in Mexico City

Congress approves the Treaty of Guadalupe Hildago ending Mexican War

Five months after the U.S. army under General Winfield Scott occupies Mexico City, the Treaty of Guadalupe Hidalgo officially ending the war is approved by the Senate.

The fighting itself has lasted for sixteen months from the opening clash along the disputed Rio Grande border at Matamoros until the final assault on the Chapultepec Castle and surrender of the capital city on September 13, 1847. Roughly 73,000 U.S. troops have taken part, with some 18,000 left dead, wounded or missing. The Mexican forces total some 82,000, but with a much higher casualty count around 35,000. 

While James Knox Polk has served as the American President throughout the conflict, Mexico has churned through five different heads of state as it contends both with the war and its own internal struggles for political power. As peace negotiations begin, the strident Mexican General Santa Anna gives way to Judge Manuel de la Pena y Pena who is eager to find a solution, despite contending with others who oppose any land concessions. 

 Meanwhile, America’s interests are in the hands of Nicholas Trist, formerly personal secretary to Thomas Jefferson, and currently Chief Clerk at the State Department. His orders from Polk are to acquire the border lands from Texas through New Mexico, together with Alta California and, if possible, the Baja peninsula – at a cost of no more than $30 million. But Trist makes his own adjustments, proposing to settle for less land along the border and excluding Baja, while offering a smaller payment of $15million. 

Polk is so upset by the changes that he recalls Trist. But that fails to stop a February 2, 1848 meeting in the Mexico City suburb of Guadalupe Hidalgo where Pena hands Trist a signed copy of the treaty. When Polk receives it on February 19, his anger over Trist’s renegade actions has receded, and he sends it along to the Senate for approval. The Whigs take their final chance to denounce the war itself before the treaty is accepted by a 38-14 margin.

In the end, the Mexican Cession adds 529,000 square miles of territory or 18% of the nation’s ultimate total (excluding Alaska and Hawaii).

Milestones In The Expansion Of America’s Landmass
YearLand AddedAcquired FromMethodSquare Miles% Total
1784 13 colonies to Miss R Britain War     888,811 29% 
1803 Louisiana Territory France Purchase    827,192 27 
1819 Florida Spain Purchase      72,003 
1845 Texas Territories Mexico Annex     390,144 13 
1846 Oregon Territories Britain Purchase    285,580 10 
1848 Mexico Cession Mexico War     529,017 18 
1853 Gadsden Purchase Mexico Purchase       29,640 
  3,022,387 100%
Mexican President Pena y Pena
Mexican President Pena y Pena
James Knox Polk 1
James Knox Polk
Chapultec Castle in Mexico City
Chapultec Castle in Mexico City

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