Well let's explain what the fugitive slave cause was. It meant that if a slave escaped they would be returned to their owner.
Now I'm unsure what you mean by sentence. I don't know if you want it used in a sentence or what the sentence was for escaping. So I'll just do both.
Used in a sentence: The slave was returned to his owner because of the fugitive slave cause.
Sentence for escaping: A slave would be returned if they escaped from their owner.