Which is one of the characteristics of a strong theme?

it is broader than the story.

Explanation:

A strong theme is not only the main idea in which a writer's work is based, it is also bigger than the story. It is probably the message the author wanted to send to his or her readers by writing the story, it might have been the objective of it all. It could have had addressed previously by the author in another work, he or she could have based many stories on that theme or may be just that one, but a theme can be addressed by many authors in many ways along history of literature.