PT 57.S3.Q12 - law backed up by effective enforcement

alkhatib683

http://7sage.com/lsat_explanations/lsat-57-section-3-question-12/

So, what's the deal w/ effective laws? How would you approach this one, in terms of a thinking through it strategy? I chose B originally, though I understood that this was not the contrapositive of the statements in the stimulus. I'm not quite getting how the international police force is a necessary condition for int law to be effective. This may be the result of mental fatigue, so please don't judge me here (: