In 1835, Mexico sought to overthrow the President Santa Anna, but the revolutions soon focused from Santa Anna, to making Texas an independent state. IN response, Santa Anna ordered his troops to execute all foreign fighters they met. On February 23rd 1836, Santa Anna attacked the Alamo with his army, where 180-260 men were waiting, including Davy Crockett and James Bowie. 2 attacks were successfully defended against, but the third attack overthrew them. For the Texans, the battle of Alamo was a symbol of their fight for independence. The Texans gained independence on April 21st, 1836.
References:
http://www.eyewitnesstohistory.com/alamo.htm
http://www.history.com/topics/alamo