The Irish potato famine

You looked in horror at the leaves. How could they have turned black overnight? With a deft hand you pulled up the plant, shaking the soil from its roots, holding up blighted potatoes, rotten on the stem.

It was too terrible to take in.

People had warned against relying on one source of food. When the blight had arrived in Europe the poor had other crops to rely on. But with the tiny amount of land you could rent, what choice did you have? Until now yields had been good; your population had risen rapidly, reaching eight million.

But now the blight had arrived. You would watch it devastate Ireland. For six years your potato crop would fail. Other crops would grow but you had no money to buy them. They would be loaded onto ships bound for England while you starved in the streets.

The British government would hesitate, send in bad grain, then stop the aid altogether, not wanting to make you dependent, deciding to let things run their course.

This was just six generations ago and yet the loss of a single crop killed more than a million people. Another million boarded ships for better lives, dying in their thousands on the way.

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.

The fall of the Mayan civilisation

Deep in the inhospitable rainforest, your glittering Mayan cities reached high above the trees, magnificent stepped pyramids surrounded by vast and bustling settlements.

Your culture evolved over three thousand years. Your sense of occasion was second to none, elaborate rituals marked by incense and chocolate and blood.

Your night sky was a window onto all possible worlds. You tracked the stars making precise calendars which told when to make war, when to sacrifice to your gods. They showed nothing was permanent; what was right in one season might not come to pass in another; understanding the past was the key to the future.

What went wrong? You thought of everything. Your complex agricultural systems fed ten million. Raised fields and terracing, forest gardens and managed fallows; rainwater stored and released by hydraulic systems.

You did not see the precarious balance you had created. When the rains failed your systems would fail. You had stripped the forest and reduced humidity. In that prolonged drought what little rain fell did not fall on you. Without reserves most of your people starved. Your few remaining cities fought each other until the jungle reclaimed the magnificent Maya cities and the memory of all you had done.