Brutus' inner struggle with assassinating Caesar is not an example of external conflict from The Tragedy of Julius Caesar, since it is an internal conflict.
On the one hand, external conflicts occurs when the character has a conflict with something outside of himself. Often these conflicts are againts another character, nature, or society.
On the other hand, an internal conflict is a problem the character has with himself. So that, the struggle Brutus has with assassinating Caesar refers to an internal conflict