Texas has made an issue over their independence and God-given right to be Texas, in defense of their the right to own chattel slavery since their first secession. From Mexico. In 1836.
Texas reconfirmed their desire to die on the hill of their divine right to own people, by seceding from the US in 1861.
After the civil war, Texas was a haven for the Confederates - and their ideology has been fomenting ever since
They've been talking of secession openly since at least the 1990s.
I think this is the first time since the civil war that other states have involved their national guards in support of a hotbed issue that could lead to a secession.
Edit: correction to grammatical error.