Why does the Wicked Witch have to die to start the journey to Oz?

My son's favorite CD right now is the Wizard of Oz soundtrack. I was thinking after he asked the question, "Why does the house have to land on the Witch?" Okay, sometimes I have good answers for such questions, and other times I am stumped. This time, I couldn't really wrap my mind around a substantial answer, but then it hit on me. My reply is as follows:

"Well, sometimes, bad things happen to bad people, and other times, perhaps they happen to good people. In this case, they actually start the story with the Wicked Witch getting killed by the house landing on her. We don't really know if she deserved it. Perhaps, no one was really nice to her and that is why she was wicked. Even so, maybe we just didn't know her well enough to know that she was really kind. Or perhaps, there was no little boy like yourself asking her to play, 'Excuse me, would you like to play with me please?' Thus, she was never really given an opportunity to be nice. In this case, the author of the story chose to kill off the witch at the begining. Some times people have to die for no real good reason."

...and here is where I get to my point.

"Why, it is a lot like invading a country for no particular reason. Like this situation in Iraq. A lot of people are sacrificing their lives, for the sake of a new begining."

...of course, this is a bit beyond a 2.5 year old kid. But hey, we have several themes laced throughout the Wizard of Oz parable that can actually help to explain to children why we are dropping massive amounts of ordinance on a people who we really don't know, and more importantly, don't know if they were wicked enough to justify their deaths.

...as I have said in the past, the ROI in Iraq is not worth the outlay.

How would you explain such things to a 2.5 or 3 year old?