When I read it, I read it was mainly just artillery shells that hit the water mainly and some parts of the city. But I could have missed something.
But really, North Koreas behavior is said by many to be "random" and this isn't the first time even before the Cheonan (spelling?) sinking. They have had some firefights many times in the past. Even at one point some NK soldiers going to SK's territory and shooting at civilians if I remember right. Even so, like said above, they have no backup anymore because China wanted to keep deals with the U.S. and Russia isn't Communist anymore.
Even if we did attack them, I doubt it would result in something like a global war. Sure, Kim Jong's supporters are fanatical for him, but the truth is, all he does is build up a military and focuses less on his people. He starves his people and they hardly have any power running through their cities. So, just as a scenario here, if we did go after them we would probably beat them quickly or by some chance they would see through Kim's lies and probably turn against him. But that is just how I think of it.
Even so, this is really more or less a border conflict compared to what was going on in the Cold War. And as Jason said, they don't really have an influence anywhere.
As for what started WWII, there was the Nazi's invading Poland, Italy becoming facsist, Nazi's attacking Stalingrad and the Japanese attacking Pearl Harbor. That is quite alot compared to what is happening today.
I know what you're thinking about though RoryFoster, but the reason, I think, people get concerned or worried is because it is probably new to them and haven't seen much history (not saying you haven't) and they jump to conclusions. In truth, the world is somewhat problem-solving now than it was back in the Cold War and WWII. My grandmother told me once that when JFK was assassinated she and her family feared the worst. But things turned out fine in the end. I also think media-hype is another reason people get so worried.
I hope this helped.
EDIT: By "fine" in my last statement I mean that it didn't cause a major conflict. Though it did raise tensions.
