Warning: A Lesson from History
The play is about Arturo Ui, a gangster who came to power in 1930s Chicago. But, Brecht parallels Ui's rise with the rise of Adolf Hitler prior to World War II. The final lines of the play tell us exactly what Brecht wants to get across to the audience,
"Although the world stood up and stopped the bastard,
The bitch that bore him is in heat again."
He is saying that we must pay attention to the corruption of successful businesses and the corruption they create in order to increase their profits. That it leaves a door open for the truly corrupt to seize control over them for fear of being exposed, which leads to the people being tormented by men like Hitler and Ui because they were not protected by those in power. They were sold out.
Greed
The Cauliflower Trust creates the open door for Ui to gain power in this play. It is their greed, their need to force what they have to sell on the market at any cost. However, the cost becomes their morality and the lives of innocent people in Chicago and Cicero. Their greed provides rise to the horror of Ui's need for absolute power, like Hitler's.
Power
Power is the central theme of Ui's neediness. He will do anything in order to be in power. He doesn't seek money like the Trust and Dogsborough. Instead, he wants to rule, and once he has a taste of even a little bit of power he desires more and more until he is beyond coming back. This is when we see Ui take his best friend's life in order to secure Cicero under his rule.
