One of the reasons this cube here looks square is because all its sides are close to us. Therefore, the vanishing points are far away from our framed page, in this case.
The cube is not square here since we changed the bottom lines and they are more inclined. Now, we can see a vanishing point because it is closer.
What will happened if we change only the bottom horizon lines of the cube and rotate them approx. 45 °? Our previous object looks like a train or a building, or something longer than a square and we have that illusion due to a long distance - right?
All parallel lines appear to converge in the distance in one vanishing point. You can see that clearly in drawings 2 and 3.
*Every object is foreshortening as much as it moves away from us.