The first important dates relating to the Mexican-American War were the start of the Texas War for Independence, specifically date on which independence was declared on March 2, 1836, the fall of the Alamo on March 6, and the end of the war not long after, which can be largely dated to the victory of Sam Houston over the Mexican army at San Jacinto on April 21 of the same year.
The United States recognized the independence of Texas on March 3, 1837, but did not immediately annex Texas as state. The date of actual annexation on which President Taylor signed the annexation document was March 1, 1845. From that date, war with Mexico became nearly inevitable.
There was a period during which reconciliation seemed possible in in September, 1845, the United States sent John Slidell was a minister with the power to negotiate the purchase of California and New Mexico. Despite having received assurance that Slidell would be welcome, he was not. In January, 1846, President Polk ordered General Zachary Taylor to advance to the Rio Grande, which was provocation that resulted in some skirmishes. The date of Polk`s war message to Congress was May 11.
A small expedition under Colonel Stephen Kearny received instructions on July 3, 1846, to go via the Santa Fe Trail from Fort Leavenworth to take over New Mexico. They reached Santa Fe on April 18, and proceeded to Los Angeles, where they arrived on January 10, 1847.
Other important dates include the capture of Vera Cruz on March 29, 1847, and of Mexico City on September 14. President Santa Ana fled, leaving some difficulty in finding competent Mexican authorities with whom to negotiate a peace treaty. The U.S. representative Trist remained even after he had been recalled and negotiated a peace treaty with Mexican ministers on February 2, 1848. The date of final ratification in the U.S. Senate was March 10.
By Charles Sumner A war of conquest is bad; but the present war has darker shadows. It is a war for the extension of slavery over a territory which has already been purged by Mexican authority from this stain and curse. Report on the War By Jefferson Davis Unfortunately, the opinion has gone forth that no politician dares to be the advocate of peace when the question of war is mooted. That will be an evil hour the sand of our republic will be nearly run when it shall be in the power of any demagogue, or fanatic, to raise a war-clamor, and control the legislation of the country. The evils of war must fall upon the people, and with them the war-feeling should originate. We, their representatives, are but a mirror to reflect the light, and never should become a torch to fire the pile. Speech in Congress, 1846 By Winfield Scott Brave rifles! Veterans! You have been baptized in fire and blood and have come out steel! After the battle of Chapultepec, September 1847