If you've ever wondered about the origins of Cinco de Mayo, here's a short article that nicely summarizes the popularity of the holiday in the U.S.:

Cinco de Mayo, from the Battlefield to the Beer Bottle

Cinco de Mayo celebrates the Mexican victory in the Battle of Puebla on May 5, 1862, against the invading French army of Napoleon III...

"Cinco de Mayo" is an official Library of Congress subject Heading. In other words, you can conduct a Subject search in Orbis, Yale University Library's catalog, and you will find several books on the holiday as well as the famous battle in the Mexican state of Puebla.  

Have a look also at the U.S. House of Representatives, Committee on International Relations', Resolution recognizing the Mexican holiday of Cinco de Mayo.

Viva México!

Today is the anniversary of the Treaty of Guadalupe-Hidalgo.  You can see an image of the Treaty on the National Archives website.

Per the National Archives, "the Treaty of Guadalupe Hidalgo, which brought an official end to the Mexican-American War (1846–48), was signed on February 2, 1848, at Guadalupe Hidalgo, a city to which the Mexican government had fled with the advance of U.S. forces.  Signed on February 2, 1848, this treaty ended the war between the United States and Mexico.  By its terms, Mexico ceded 55 percent of its territory, including parts of present-day Arizona, California, New Mexico, Texas, Colorado, Nevada, and Utah, to the United States."  In sum, Mexico ceded 525,000 square miles (55% of its pre-war territory, not including Texas) to the United States in exchange for $15 million ($313 million in 2006 dollars).

The library has several items specific to the treaty including:

• The Treaty of Guadalupe: A Legacy of Conflict (1990)
  
• The Treaty of Guadalupe Hidalgo: 1848-1948 (1948)
  
• Treaty of Guadalupe Hidalgo. Message of the President of the United States, transmitting a communication from the Secretary of State, and accompanying papers, in compliance with resolutions of the House of Representatives, of the 5th Instant, relative to the Treat of Peace concluded at Guadalupe Hidalgoon the 2d of February, 1848 (1848)

The Library of Congress has assigned a subject heading for material related to this treaty: Guadalupe Hidalgo, Treaty of, 1848. 

Yale's Avalon Project also has the full-text of the treaty.

U.S. Treaties prior to 1950, such as the Treaty of Guadalupe-Hidalgo (9 Stat. 922), were published in the Statutes at Large.  Volume 64, Part 3, contains an Index of all treaties ratified by the United States prior to 1950. 

Treaties to which the U.S. is a party are now published in United States Treaties and other International Agreements.

http://faculty.umf.maine.edu/~walters/web%20103/map%20guadalupe%20hidalgo.gif