Let me be the first to poo-poo on this thread by saying I hate Texas history. I was gathered with several friends recently and we were all lamenting over the mandatory year of Texas history we were put through (I believe in 7th grade?) -- a whole year of cowboy folklore and frontiersmen mythos. Ugh. It's a whole year that could have been spent on, god forbid, world history instead of something as insignificant and nationalistic (statist?) as Texas history.
Here in Oregon, they teach Oregon history. But at least it is in 4th grade and all they do is make Native American dwellings with popsicle sticks and pretend they are on the Oregon Trail for a couple of weeks. I do remember 7th grade Texas History though... I enjoyed it. Probably because I enjoyed History and had a great teacher.
Not impervious: ie, more powerful than all others combined, but certainly most powerful on a pure ranking. Our most dangerous enemies militarily are Russia then China; but they've both collapsed internally when fighting wars abroad. Whatever we lack in ceremonial patriotism we make up for with sheer obliviousness to other cultures.
Your teacher dropped the ball. Texas history should be a perfect tie-in to late Renaissance, Latin American, frontier and Civil War history. The two problems are that they undo their own curriculum by showing all the damn Alamo movies; and that they haven't figured out a cohesive, compelling narrative for king cattle, king cotton, building the University system, the energy industry and each big city's individual period of rapid growth.