"Uncle Bran says that it's what connected Earth to the rest of everything... I guess it's like the Force maybe... but a long, long, long, long, long, long, longlonglonglonglonglong looooong long time ago humans messed something up and cut Earth off from it."

It happened a very long time ago. Asking her for details won't get much because she's five and doesn't know. She knows that it exists, much like any kid would know that galaxies exist, but if she were asked to explain exactly what it was...

She licked her fingers free of the chocolate. Before eating another one.