The introduction of smallpox into the New World

You set out to conquer the New Worlds, small groups of adventurers seduced by the promise of gold beyond compare. You pictured those vast virgin territories laden with riches; you would claim them all. You had right on your side; you were Christians. You had might on your side; guns and horses and fighting dogs to charge into battle.

But it was another deadlier weapon that brought you victory in the end. The Old World diseases you carried were an invisible threat to these people who had lived less festering lives.

Mostly it was accidental. A slave took smallpox to Mexico. The disease killed up to half the inhabitants in the Aztec capital in a year, sweeping through the country. ‘The great dying’ reduced the population from twenty million to three million over the next fifty years.

But some of it was deliberate; you gave blankets from infected corpses to the Native Americans in 1763.

Mortality rates were high: Piegan, Huron, Catwaba, Cherokkee and Irquois - 50%, Omaha and Blackfeet - 66%, Mandan 90%, Taino 100%. Those who survived were more often than not maimed or blind or infertile.

If you ever looked back you would have seen your conquering dream realised in ways you could never have imagined.