I agree with much of what has been said above, but cannot agree with the idea that area rule has nothing to do with the wings. This is simply not true.
The aim of area ruling is to reduce transonic drag by delaying the formation of shock waves (increasing MCRIT) and by reducing the intensity of the shock waves when they eventually form. To understand how this is achieved it is necessary to look at what causes shock waves.
The local speed of sound (LSS) is the speed at which pressure changes move through the air. When a series of pressure changes move upstream through an airflow, their velocity relative to space is reduced by an amount equal to the velocity of the airflow.
If the pressure changes reach a point where the airflow velocity is equal to the LSS, the speed of the waves relative to space is reduced to zero. This causes the changes to pile up on each other at the point where the air velocity is LSS. In this condition the values of all of the changes are added together to create an instantaneous larger pressure change.
If the pressure changes were decreases in pressure the effect would be a sudden decrease in pressure. This would not from a shock wave. If however the changes were increases in pressure, the piling up of succeeding changes would cause an instantaneous increase in pressure. This sudden increase in pressure is a shock wave. Air passing through a shock wave is decelerated and its temperature increases. This increase in temperature cause a loss of total pressure energy in the airflow. The overall effect of this process is increased (wave) drag, whcih adds to the total drag of the aircraft.
The important thing to note in this sequence is that shock waves and the resulting wave drag occur when pressure INCREASES meet sonic or supersonic airflow. Pressure decreases meeting such airflows cause no such problems. So to reduce wave drag we must reduce pressure increases around the aircraft.
The second point to note is that shockwaves cannot form if the airflow velocity is less than LSS. As an aircraft moves forward, the air must move aside to let it pass. This causes the flow accelerate around areas of surface curvature. The local air velocity at any point on the aircraft is equal to the TAS of the aircraft plus whatever acceleration has been caused by the structure. So to achieve the greatest TAS without any airflows reaching LSS, we must minimise the acceleration rates of the air around the aircraft.
The accelerations are proportional to the rate of change of cross section of the aircraft, so minimum accalerations require minimum rates of change of cross section. So by reducing the rate of cross sectional area, the area ruling process increases the TAS at which the first shockwaves form. This delays the onset of wave drag until the aircarft has reached a higher TAS.
But the process does not stop there. Broadening the fuselage ahead and behind the wing roots, and narrowing it at the wing roots, fin roots and tailplane roots, reduces the rates of pressure increase and hence shock wave intensity in these areas. To understand this we need to look at what the air is doing as the aircraft passes.
Air which is moved aside to allow the aircraft to pass, must move into space which is already filled with other air. The overall effect is that the air is compressed and its static pressure increases.
If a lot of air is pushed aside, the increase in pressure and hence shock wave intensity will be large. These stong shock waves will cause a lot of wave drag.
But narrowing the fuselage at the wing roots, provides additional space for the air to move into. This reduces the overall increase in pressure and the resulting shock wave intensity. These weaker shock waves produce less wave drag. So by varying the fuselage cross section to match the position and cross sections of the wings, fin and tailplane, wave drag is delayed and reduced.
Although this process has been used in many aircraft, it was particularly evident in the old Northrop F5. Not only was the fuselage waisted, but also the wing tip fuel tanks. It is an indication of the effectiveness of this process that many such aircraft types performed better with external tanks fitted than without them.
Supercritical wings can be said to be an extension of area ruling. In this case the formation of shock waves is delayed and the accelerations over the wings, shock wave intensity and wave drag are all reduced by reducing the camber of the upper surfaces.