The terrorists had used their influence — fear— to keep the women as prisoners.
The power of believing in the myth (fear) kept its spirit alive.
How should these types of examples be punctuated? For instance, if you want to draw attention to an idea or meaning not explicitly understood.
Commas are the simplest choice, and the one you should use by default.
Dashes indicate a more significant break in the flow of language or the flow of ideas. Dashes create a more dramatic effect on the page. Use with some caution.
Round brackets should be used for additional information that can be ignored by the reader without affecting the meaning of the text. Your document should be readable and sensible if the material inside the brackets was simply deleted.
But there is no rule that says "in this situation you must..." so you should use your judgement.
