Cassius persuades Brutus to join the conspiracy against Caesar in an effort to save the Roman Republic from Caesar's perceived tyranny and to restore democratic governance.
Cassius is trying to convince Brutus to join a conspiracy against Julius Caesar because he views Caesar as a tyrant who threatens the Republic's democracy. The political situation in Rome was tense due to Caesar's considerable accumulation of power.
After being appointed dictator and receiving a term for life, many senators, including Cassius, feared Caesar's growing autocracy, stemming from a history of Roman distrust toward authoritarian rule. With the assassination led by Brutus and Cassius, they aimed to restore the Republic and prevent Caesar's potential despotism.
The probable question may be:
"In Julius Caesar, Why is Cassius is trying to convince Brutus to join a conspiracy against Julius Caesar?"