In fact, you can determine the theme by looking closely at other literary elements involved, such as, characterization, setting, events, point of view, tone, irony, imagery, etc. In other words, theme is illuminated through these literary elements. Explain how Julius Caesar is in part the story of the conflict between Brutus' ideals and the real world. Too much ambition inevitably leads to disaster. Politicians are concerned with power than issues affecting people's lives.
Violence leads to more violence.
Crowds can be easily manipulated and moved to violence. Violence begets violence. When legitimate authority breaks down, all other rules of society will crumble too. Begin your introductory paragraph with a thesis statement, which restates the main idea of the assignment. Be sure to state the theme in terms of a generalization about human nature or experience.