How much does a nuke destroy?

When I was a kid, I always thought a nuclear bomb could destroy a complete country. It was only a couple weeks ago, I read about nukes on wiki. No , I was sure a complete county was out of the question, but how much does a nuke destroy?

So first of all, the only bombs ever used, were the ones thrown on Nagasaki and Hiroshima. Why didn't the Americans threw one on Tokyo? Because those cities were made of wood. Most of the houses and buildings are thus not strong and that means more damage (and kills).

The biggest bomb ever build by humankind was the “Tsar bomba”. It was way more powerful than the nuclear bombs that were thrown at Hiroshima and Nagasaki. To test this bomb the Russians flew it all the way to Nova Zembla in an airplane. The thing didn't even fit in the bomb bay, so they left the bay doors open.

How “bad ass” was the explosion? Well pretty bad. The mushroom cloud was 60 km high. The fire ball was 4.6 km wide (fat man's, on Nagasaki, was 200 meters). And don't think standing 100 km away would have been a nice viewing experience. You would have had third degrees burns.

Right now, we (as humans) don't have such big bombs anymore. The cold war is over. Since then the USA and Russia have been dismantling there bombs. According to wiki in 2006 Russia had “only” 15.000 and USA 10.000 nukes left.