HELPING THE OTHERS REALIZE THE ADVANTAGES OF GAS PISTON AR PISTOL UPPER

The e-book 'Guns, germs and steel' released me to The very fact that the Sahara desert in fact isolated Sub-Saharan Africa from the developments elsewhere because the start of civilization until eventually European colonialism. My main issue: is this correct? Had been there main isolated exchanges of information?@Roger V.'s answer is often a good a