It is probably from the house settling at some point, and might not indicate anything that needs attention (especially since it has been stable for some time), although I usually see such cracks emanating from a corner of the window rather than straight across the wall.

Because the crack divides the wall, I would be on the side of caution and get a pro in there to look for issues in and around that wall. Things like slab subsidence or termites come to mind. Also, check outside to be sure that all water is directed away from the house - water collecting at the foundation can cause shifting in walls, and that does need to be addressed.

Gable end walls move around a good bit. If it doesn't enlarge, its not likely anything to be worried about.

Since it's so straight, I am guessing that it is a seam where two pieces of sheetrock meet, and it’s caused by a little bit of movement or settling. I doubt it is anything structural. I wouldn't be surprised if you measured the height of the crack and found it was about 48" high ;-)

Check your inspection report and see if it was mentioned. Are there any corresponding cracks on the exterior?

The inspection report does not mention it, and i'm pretty sure it was there during the inspection.

There are some vertical thin cracks in the slab on the outside. Those were there during the inspection. They don't correspond with the interior crack.

both are normal in many cases.