Humanity has lived through some horrific periods in history, including natural disasters, plagues, and man-made crises. Plagues have threatened to wipe out civilization more than once, while famine, floods, and fires have brought devastation and destruction. Wars, depressions, and atomic weapons have also contributed to the darkest times in human history. How did the world recover from calamities like the Black Death, the Great Depression, and the Spanish flu?