Well, I guess it's the whole terrorisim thing. They're not reliant on defeating the enemy through brute force but in causing them to cave to pressure out of fear or make a wrong move with a knee-jerk reaction. If the bastards are serious about taking out a nation they need to use gorilla tactics and target easy weak points of high value that would cause damage to the country's finance and infrastructure. I mean, why blow up a train, yourself and a few dozen people when you can probably cause just as much havoc by planting a smaller explosive on the rails at a point where the train is at top speed. Boom, train derails, wrecks it's self, kills dozens and holds up the public transport just as easily (You don't even need to blow yourself up, although you'd probably still get caught). Heck, steal your way into coal mines, throw some accelerant onto a mountain of coal, light a match and there goes hundreds of millions worth of resources and expense to extinguish the blaze.
There's my next destroy the world bid. Transport biological diseases through customs. Just chuck some infected plant matter with Citrus Canka in your pocket, spread it 'round the country side and you destroy vast quantities of food for the world. Add mad cow's disease to the list and maybe the avian flu if you can get it and there's food shortages and wide-spread panic. When they detect a few infected animals or plants they destroy the entire crop and every neighbouring crop for miles in a bid to erradicate the pest.
Food shortages and price hikes lead to panic and econimic disaster. Wars break out in the frustration and desperate bids. With luck, nukes fly and it's all over. Bit of a long-shot to get all the way to nukes though.
C'mon, who else has plans to destroy the Earth?