Actually launching an all-out attack on Seoul and invading South Korea with the million man North Korean army is not the ultimate vision of dictator Kim Jong-il-a vision secretly shared by the mullahs in Tehran. Both regimes are working in concert and at a furious pace to implement a "doomsday scenario" for their mutual enemy: the United States of America.
David and Goliath
US strength is being tested daily. From its weakened economy, the perilous situation in Europe, two ongoing wars and fending off asymmetrical warfare against terrorist networks like al-Qaeda, to preparing for a future cyber war, America has it proverbial hands full and its resources scattered all over the globe.
According to Western intelligence sources, several years ago Kim Jong-il's military analyst discovered one of America's greatest Achilles' Heels: the superpowers reliance on computer technology.
The computers that the US uses to keep 21st Century America moving are simultaneously one of its greatest assets and one of its greatest potential weaknesses. A potential cyber attack from Russia, China or some other state weighs heavily on the minds of the military personnel involved with war game scenarios.
The nuclear EMP weapon
"An EMP that results from a nuclear weapon ... destroys any 'unhardened' electronic equipment and electric power system--which means virtually any civilian infrastructure in the United States. The pulse occurs when a nuclear weapon explodes ... at an altitude between 40 and 400 kilometers.
"The detonation of the nuclear warhead releases ... energetic particles [that] scatter in every direction away from the blast. Many of the particles descend and interact with the magnetic field lines of the Earth, where they become trapped. The trapped electrons then create an oscillating electric current within the field, which rapidly produces a large electromagnetic field in the form of a pulse.
"Once the pulse reaches electronic equipment, it negatively interacts with them and either disables, damages, or destroys them. An EMP generated by a nuclear weapon could affect all critical infrastructures that depend on electricity and electronics within the vicinity of the nuclear warhead blast radius. A nuclear weapon with a burst height of approximately 100 kilometers could expose objects located within an area 725 miles in diameter to the effects of EMP." 
Why the US computer network is at risk
All this could occur with one well-placed nuclear detonation above the West Coast or western Midwest. The failures would cascade like dominoes and knock out the entire electrical grid of the US and maybe most of Canada and Mexico too.
US preparedness and comprehensive planning for an EMP attack remains woefully underdeveloped despite persistent warnings, such as the one in the 2006 Quadrennial Defense Review that the "expanded reliance on sophisticated electronic technologies by the United States, its allies and partners increases their vulnerability to the destructive effects of electromagnetic pulse (EMP)."