Why Are Northern Countries More Successful Than Southern Ones?

What’s a Roman centurion doing all the way up north in England?

Why are countries in colder climates more successful than warmer ones? The French philosopher Montesquieu answered this question back in 1725:

cold air constricts the extremities of the external fibres of the body; this increases their elasticity, and favours the return of the blood from the extreme parts to the heart. … People are therefore more vigorous…