In general, we can say that the central idea of "The wonderful wizard of oz" is that good is more powerful than evil and will always be victorious.
The author does this through the literary technique of developing archetypes. An archetype is a very well-defined and generalized model of behavior. We can see this in "The wonderful wizard of oz" because the author leaves characters very well defined with good behavior patterns and bad behavior patterns. Good characters always achieve their goals and evil characters always get defeated, no matter how much they try to succeed at something. This becomes even more evident when Dorothy, who represents the archetype of good, defeats the Wicked Witch of the West, which represents the archetype of evil. Dorothy defeats the witch even though she doesn't have special powers and abilities, just using the force of good.
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well stockyards mean a large yard containing pens and sheds, typically adjacent to a slaughterhouse, in which livestock is kept and sorted. and i'm assuming that by party you mean a large group of people which does make sense because chicago is a very crowded place much like new york. stockyards tend to take up a lot of room due to needing the area for pens to keep animals in and the fact that stockyards are usually right by slaughterhouse where they process and distribute the product. so its much like a zoo but with some dead animal products close by.