It was 1836, not 1835, and the disagreement was not about slavery. The Spanish, and later, the government of Mexico, had a scheme, attested in the archives in Mexico City, to admit immigrants, mostly Scots-Irish, to colonize Texas, AKA "Comancheria' and form a buffer between the Comanche, who had gotten the use of horses, and thus become a real menace, and more settled parts of Mexico. The plan had a further stage, raising taxes on the gringos, to drive them back out of Texas, once they had dealt with the Comanche. Santa Ana, having so little knowledge of Texas, thought that he could further this plan, by abolishing slavery. He did not know that the Scots-Irish were mostly freehold farmers, who did not own slaves and some of them, like my family, were Abolitionists, before Abolitionists were really a thing in the USA. There were revolts at about the same time in several Northern Mexican states, none of them about slavery, AFAIK. They all hated the dictator Santa Ana, but only the Texans were successful in our revolt. Remember, they had admitted us because we were such effective Indian fighters. Sam Houston, who sometimes lived among the Indigenous Americans for years at a time, was also very effective when he warred with some of the tribes who had never been as friendly to him. He absorbed a goodly bit of Indigenous tactics, like fighting from cover, ambush, and more than I could know. He used this knowledge to win the Revolution. You should hear my grandchildren recite the story of San Jacinto, as taught by their Grandpa. The four-year-old is still learning, but the other three are so cute, especially when they tell about the charge into the Mexican camp, shouting "Remember the Alamo. Remember Goliad," defeating the fourth largest army in the world at that time, and thus securing the blessings of Liberty for themselves and their posterity, including us. We flew our Texas flag yesterday, and we'll hang it out again on the 21st of April, San Jacinto Day. "Don't mess with Texas" is our anti-litter slogan, but, well, it might have a more general application.
Happy Independence Day to you! You are correct. Slavery was not the issue and Mexico never really controlled Tejas. The Comanche did. The Comanche were almost driven to extinction after they were driven out of Wyoming by neighboring tribes in the 1600s. They headed south and eventually ran into Spanish settlements. Getting Spanish horses, however, more than leveled the playing field. The Comanche gave out revenge on the Spanish, Mexicans, French, and any Indian tribe that ever slighted them. The Comanche beat the bejesus out of the Mexicans, although they did have a sort of truce with New Mexico cities (they needed a place to fence goods and captives/hostages and buy weapons). The Anglo Texans, fought a war of attrition with them for fifty years, mainly by adopting their same hit and run tactics. It was only with repeating arms (thank you Samuel Colt) that the balance of power tipped decisively and they were eventually defeated.
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