Betrayal. Brutus places his ideals (Rome as a republic) over his friend, Julius Caesar, and is willing to kill Caesar to protect the Republic.
Fear. Incredibly afraid of losing Rome as a republic, Brutus is willing to murder Caesar before the guy even does anything wrong. In his mind, it's better to sacrifice an innocent ruler than risk his becoming a tyrant.
Political Turmoil. Things don't go according to plan. The politicians are like, "the citizens are going to kiss our togas for eliminating the tyrant Caesar! Down with absolute power." But the citizens are like, "What! You killed Caesar? We loved him." Let's just say that the politicians aren't exactly tuned in to the citizens' wants and needs.
Reason vs. Passion. With his clear logic, Brutus convinces the concerned public that Caesar was a tyrant who needed to be eliminated in order for them to be free. Then along comes Antony, with his passionate, emotional appeal, who just as easily swings the public in the other direction, turning them into an angry mob determined to avenge their beloved Caesar.
Sacrificing Personal Morals for the "Greater Good." Brutus is well-known for being a moral and honest guy, yet he decides to commit murder and sacrifice his morals in hopes of ensuring a better future for Rome.
We're sure you can find other intense issues from the play that are highly relevant to our modern world. Chew on these questions for us, and fill in the blanks about how each of these points resonates with your personal life, your experience at school, or even in the country or world as a whole. It seems like the real question is: how can you not care about Julius Caesar?