Today is a significant day in Texas and American history. On this day in 1836 Sam Houston's Texians caught Santa Anna's Mexican army literally sleeping; they were at afternoon siesta when the attack came. Santa Anna was said to be entertaining Emily Morgan, the Yellow Rose of Texas, in his tent. The Texians suffered two killed while several hundred Mexicans were killed, and Santa Anna was captured. Since he was the dictator of Mexico, Houston forced him to recognize Texas' independence in return for his release. Thus was born the Republic of Texas.
This event led eventually to the Mexican War. Texas was annexed into the United States in 1845 and Mexico did not recognize Texan sovereignty. This led to the conflict in 1846-1848. As settlement for the war the Treaty of Guadalupe Hidalgo led to the Mexican Cession. The Mexican Cession added approximately a third to the size of the then United States; added territory included California, Nevada, Arizona, New Mexico, parts of Texas, Colorado, Utah and Idaho.
The events of April 21, 1836 truly had long range affects both for the U.S. and Mexico, and all because Santa Anna did not prepare to defend his army.