What were the major events that led to texas joining the union

The Texas Revolution or Texas War of Independence was fought from October 2, 1835 to April 21, 1836 between Mexico and settlers in the Texas portion of the Mexican state Coahuila y Tejas. Animosity between the Mexican government and the American settlers in Texas (who were called Texians), as well as many Tejas residents of Mexican ancestry, began with the Siete Leyes of 1835, when Mexican President and General Antonio López de Santa Anna abolished the Constitution of 1824 and proclaimed a new anti-federalist constitution in its place. The new laws were unpopular throughout Mexico, leading to violence in several states. War began in Texas on October 2, 1835, with the Battle of Gonzales. Early Texian successes at La Bahia and San Antonio were soon met with crushing defeat at the same locations a few months later. The war ended at the Battle of San Jacinto where General Sam Houston led the Texian Army to victory in 18 minutes over a portion of the Mexican Army under Santa Anna, who was captured shortly after the battle. The conclusion of the war resulted in the creation of the Republic of Texas. 

I think the main reason was Mexicans coming across the border and trying to invade them ! 
Hope it helps :)