Disclaimer: I was born and raised in Houston.
In the part of town that I lived in, which was the Energy Corridor along I-10 between Beltway 8 and George Bush Park, racial tension was pretty harsh. You had haves and have-nots. Most of the have-nots were notably of one culture or another (depending on which block you were on), and they were pretty merciless about taking advantage of the haves, which were also a monoculture based on the area.
Houston was the first place I've had my car broken into repeatedly, to the point that I started leaving the doors unlocked and the windows rolled down regardless of weather. (A plastic seat cover is cheaper than new windows.) Houston was the first place that I've been very happy that I owned dogs, and considered owning a gun. I grew up not locking doors; Houston made me form a routine of checking doors, security bars, deadlocks, door blocks, and window locks and setting the alarm before bed. The Energy Corridor was NOT cheap to live in, and we rented a modest sized house. That part of town has 1980s era architecture where few, if any, windows face the street. I grew up with block parties and knowing your neighbors and talking at the mailbox. Everyone in my neighborhood in Houston, regardless of color, rolled right into the garage and the door came down.
I don't know why it's that way, but I suspect it was that cultures self-segregate instead of mix. Personally, I hope to never need to find out, because I'm not coming back, even to visit.
Additionally, note that there was an (arguably recent) influx of folks from New Orleans during Hurricane Katrina--that had lasting economic and demographic impacts on large parts of Houston, especially around Reliant.
I used to live across from Reliant a few years ago--many neighbors were folks that had resettled in Houston from New Orleans.