Texas gave up that land so they could keep slavery:

“When Texas sought to enter the Union in 1845 as a slave state, federal law in the United States, based on the Missouri Compromise, prohibited slavery north of 36°30' parallel north. Under the Compromise of 1850, Texas surrendered its lands north of 36°30' latitude.”

Tell me more about how critical race theory shouldn’t be taught in school.

I am a grown ass man and I just learned about this 5 minutes ago.  Fuck everything about trying to hide the sins of our past.

Critical Race theory, as it actually is, is a high level class taught in Law School. It focuses on how laws in the US that are supposed to be equally affect everyone, actually disproportionately affect marginalized people.

What the is displayed in OP's image is US history as it is related to slavery.

When certain conservatives are crying about "Critical Race Theory," they are complaining that they don't want certain kinds of history taught in school. Anything that might make people feel bad. Making history nice and palatable instead of actually acknowledging the messy realities.

The making of those past mistakes isn't the problem. It's the fact that so many people are unwilling to own up to those decisions. By making it problematic to teach about certain aspects of history, they will be able sweep under the rug atrocities that are still effecting people to this day.