Hernan Cortes fled the Aztec capital Tenochtitlan in 1520 under blistering military assault, losing the bulk of his troops on his escape to the coast.
But the Spanish conquistador unknowingly left behind a weapon far more devastating than guns and swords: smallpox.
When he returned to retake the city, it was reeling amid an epidemic that would level the Aztec population, destroy its power structures and lead to an empire’s brutal defeat — initiating a centuries-long annihilation of native societies from Tierra del Fuego to the Bering Strait.
