This w/u has been put together and refined from some old, messy w/us by GypsyBill, dolphinboy, and opteek.
Nikola Tesla was a truly unusual genius. Electricity was his specialty; he understood it like no one else. Here's a theory on how to take over the world using a Tesla coil.
Now a basic principle of electrical engineering is that the ground is an electrical sinkhole, where energy returns to. But what would happen if the ground was suddenly reversed and became a source of energy? Here's what could happen, and how its done.
Get or build yourself an extremely powerful Tesla coil and some kind of massive power source. Here's the concept behind your chaos: when electricity is "sunk" into the ground it travels much like a ripple in a pool of water, travelling through the earth and bouncing back to the point of origin. By correctly timing the discharge of electricity from your Tesla coil, you can continue amplifying your electric ripple until it builds up to great strength. (HongPong note: wouldn't the energy travel back to the power plant?)
Supposedly, Tesla got a 56 ft lightning bolt to come off of his lightning rod, before his power was suddenly cut. At time, Tesla was receiving free power for one reason or another (Either he had a relative working at the power plant or that they were aware of his research and wanted to contribute). During the experiment, Tesla blew out three power generators, and the power company shut off the power. Tesla immediately phoned the power company demanding to know why they had interfered with his experiment. The power company explained the situation and said that it'd be a cold day in hell before they'd give Tesla electricity again.
Think about it: that electrical energy is hitting the other side of the earth... be that in a city, the ocean, or an arsenal. You could demand payment of ONE MILLION DOLLARS or have large cities face destruction. Some say that the famous Tunguska incident was actually caused by an experiment like this. It is also possible that one could use a large oscillator to determine the resonating frequency of the earth, and use this Tesla coil methodology to shatter it, or at least make massive earthquakes. Then again, with all the different layers (mantle, core, etc.) could the earth have a resonating frequency?
There is another theory which states that properly pulsed Tesla coils can bend space-time and change the state of matter itself, but hey, I say try and do it. :P
For more info on taking over the world with electromagnetism, see the related Tesla tower, and maybe the Philadelphia Experiment and Schumann resonance.