On the Level: What causes drywall cracks and how to fix them

I have a vertical crack in the drywall wall from the floor to the window sill in a window in my living room. I walked around the outside of the house but couldn't find any corresponding cracks on the exterior in that location.

The house is covered in siding which may and probably conceals any cracks. Several years ago, we had minor cracks visible on the exterior of the foundation. We had someone check them out (just settlement we were told) and then repair them. On my walk-around today I noticed that some of those cracks are evident again. In the laundry area of our unfinished basement, there is a good-sized vertical crack in...