The capture of a battalion of United States troops by Mexican forces on the Texas side of the Rio Grande, the disputed boundary, followed by an expedition into Mexico proper by General Zachary Taylor precipitated the Mexican war. When reports of these events reached Washington, Congress on May 12, 1846, passed “An Act providing for the prosecution of the existing war between the United States and the Republic of Mexico". The following day, the act was approved by the President, who issued his proclamation that war existed between the two republics. The Mexican Congress declared war against the United States May 23, 1846, before our declaration was known in Mexico. A treaty of peace between the United States and Mexico was tentatively agreed to at Guadalupe Hidalgo, near Mexico City, February 2, 1848, when hostilities practically ceased. After some modification of the terms, the treaty was ratified by the United States on March 10 and by Mexico on May 30, 1848. Peace was officially proclaimed by President Polk on July 4, 1848.
Davis, T. Frederick
"Florida’s Part in the War with Mexico,"
Florida Historical Quarterly: Vol. 20
, Article 3.
Available at: https://stars.library.ucf.edu/fhq/vol20/iss3/3