The major reason Texas wanted independency:
Many of the Anglo-American settlers owned slaves. Texas was granted a one-year exemption from Mexico's 1829 edict outlawing slavery but Mexican president Anastasio Bustamante ordered that all slaves be freed in 1830.To circumvent the law, many Anglo colonists converted their slaves into indentured servants for life. By 1836 there were 5,000 slaves in Texas.
In 1836, the Texans adopted a constitution that formally legalized slavery. The Republic of Texas included the area of the present state of Texas, and additional unoccupied territory to the west and northwest. Most Texans wanted their Republic to be annexed into the United States. However, strong abolitionist opposition to adding a slave state blocked Texas's admission until pro-annexation James K. Polk won the election of 1844.
The Nueces massacre was a violent confrontation between Confederate soldiers and German Texans on August 10, 1862 in Kinney County, Texas.
German Texans tended to support the Union and had few slaves. Gillespie and other central Hill Country counties had voted against secession. By August 1862, a party of 61 German Texans from the Hill Country counties, who were fleeing to Mexico, was overtaken by the Texas Confederate cavalrymen on the Nueces River. Shots were fired and as a result 34 German Texans were killed, with some being executed after being taken prisoner. The Germans from Central Texas were fortunate to avoid such violence. They successfully traveled to Mexico City under the leadership of Paul Machemehl of Austin County.
The Treüe der Union ("True to the Union") monument to the German Texans slain at the Nueces massacre was dedicated on August 10, 1866 and sits in Comfort, where the remains of the Unionists are interred. It is the oldest Civil War monument in Texas and the only one dedicated to Union sympathizers in all of the former Confederate States of America (apart from national cemeteries).
Sources, look Wikipedia or book. I'm too tired to argue with hicks right now.
One of the worst atrocities of the Civil War in Texas happened to a family that first settled about 2 or 3 miles from where I live. I think it was a guy whose last name was Sawyer, his brother, step brother, and 2 others were on their way to Mexico, when a group of confederates caught them. They then after getting drunk hung them. (not like kicking off the horse and breaking your neck,
actually roping them up on the ground and letting them suffocate.) I dont know if it was ever charged though.