What should I do with this long 1/2 wall to make it not look so long?

You can remove it and install some sort of wrought iron railing. I gather it's a staircase on the other side? Removing the trim squares and/or painting the wood the same color as the wall will also make it less noticeable.

What about a floor plant on one end and a low bookcase or small table along it. I agree about removing or camouflaging the square trim by painting it the wall color.

It looks great to me. How about some sort of decor in front to break up the expanse?

Paint the half wall and the one behind it a darker (but the same) paint color in a flat finish to make them blend, which will visually make the half wall disappear. Another idea is to use texture on both (textured wall paper like grass cloth) or a faux stone veneer. The key to making the half wall disappear is to make it blend with its surroundings. Right now the wood trim draws your eye right to the feature you don't want to emphasize..

I would use one of the slim console tables that are quite popular, now. It would break up the expanse of wall without disrupting the traffic flow.

Agree with Fiddledd224 that right now because there is nothing of interest along the whole wall, or in the left hand side of the room, other than the square trim on the half wall, that is where your eye is drawn to. Also, right now the decor of the room is very imbalanced- all the stuff is on the right side surrounding the fireplace.

Paint the trim and the rest of the wall in the same color so that you can begin with a clean slate, so to speak. Then, on the wall behind that half wall (the back wall of the stairwell?) put eithor a large mirror, or some bright colourful artwork, or something 3D shape. Whatever you choose though, it must be large, otherwise it will just look itty bitty and will not be effective in balancing the visual weight of the fireplace.

I totally agree taking down the trim on that short wall along with top and bottom trim and you need a focal point in that room which would be the fire place. Paint the fireplace wall a accent color from your throw pillows. Not seeing where the placement of your furniture is now or the tv, I would place two sofas facing one another with center coffee table and a colorful area under that table. Place sofa table behing the sofa as you enter from that wall. This will camouflage that wall. I have photo idea of the things I mentioned. You could wall that right off too, just a thought.

I found this too

In order to break up the seeming length of this staircase(?) wall you need some verticality. I would suggest hanging some kind of pictures on the wall on the other side of the staircase. This is a terrible photo but still illustrates what I mean. You should hang a number of pictures but so there are more going down than across. You want the wall to look longer. That will "lengthen" the short wall in front. I would not remove the trim on the short wall, that is the only thing that now is keeping that wall from appearing even longer!

Maybe a book case even with the heigh. Most definitely pull the squares and not pull your eye toward it. It should blend in

Put large potted plants or trees in front of it.