>>44267
>Like between Algeria and Libya. In their case I'd assume the coastal region is inhabited, while the inner deserty parts are sparsely. Are their coasts so different? What made Algeria so populous? Libyan people don't have sex?

Maybe it is historical differences - Algerian coast had better development from ancient times, maybe trade and close proximity to Italy/Spain matters.

Considering demographics - they've both had typical high birth rates and fast growth, but Libya had less people when that demographic epoch (modernity with tech and proper healthcare), and so it needs more time for growth to became noticeable. That type of growth is exponential, so initial amount matters. Compare Nigeria and Gabon - they both got near 5x population (from 45 to 200 and from 0.5 to 2.2), but what a difference in absolute numbers.