<span>Well, I think it's by contemplating the purpose and structure of government. I hope this is what you're looking for.</span>
It dried up.
North Africa used to be a fertile grassland, even swampy in some spots, 12,000 years ago. By 1000 BC (actually quite a while before) it had dried up into what is the the largest desert i the world: the Sahara.
An isolationist no problem and seriously this is the right answer.
I believe that the answer is b