Sometimes bad can be good

The latest from Nathan Nunn:

"Because rugged terrain hinders trade and most productive activities,
it has a negative direct effect on income. However, in Africa rugged
terrain afforded protection to those being raided during the slave trades.
Since the slave trades retarded subsequent economic development, in
Africa ruggedness also has had a historical indirect positive effect on
income. Studying all countries worldwide, we find that both effects
are significant statistically and that for Africa the indirect positive effect
dominates the direct negative effect."

The full paper is here and it is recommended.