Understanding the area rule
 

Can someone explain how the area rule works?

Say, when a plane has forward swept wings, the fuselage ought to narrow sharply well ahead of the wing root, at a line with wingtips, so as to conserve the total cross-section. But when the plane is at nearsonic speeds, is the airflow around the fuselage particularly influenced by what is going on far away at the wingtips? (After Mach 1, the airflow cannot be affected at all...)

I was about to start explaining but the I saw this:

http://www.pprune.org/forums/showthread.php?t=9950

No way I could do better.