And the purpose of it?
Most of the fighters were a response to the Cold War. The Soviets and the US were in a race.
Now, with no other superpower threat, one can only wonder why these things are being built. Air supremacy can be maintained in Afghanistan and Iraq, for instance, and about anywhere in the world with the current models of fighter aircraft. The electronics can always be enhanced. Look at the B-52.
It seems to me it's an example of the "military-industrial complex" tail wagging the US dog, with it's only use being offensive with all that implies.
Arf