A grove of trees at Mount Auburn Cemetery now covers a mass grave of several hundred African Americans victims of the 1918 influenza pandemic. Tribune News Service

Joe Mozingo, Tribune News Service

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.

From the Plague of Justinian and the Black Death to polio and AIDS, pandemics have violently reshaped civilization since humans first settled into towns thousands of years ago. While the outbreaks wrought their death tolls and grief, they also prompted massive transformation — in medicine, technology, government, education, religion, arts, social hierarchy, sanitation. Before the cholera epidemics of the 19th century, cities thought nothing of mingling their sewage and water supply.

No one can know exactly how the COVID-19 pandemic will ultimately change the world. Unforeseen consequences will lead to even more unforeseen consequences.

But stress cracks are already showing. Nations are turning inward. Rulers are seeking more authoritarian power. The decline of American leadership is accelerating. Economies are facing recessions. People are living in fear and distrust, with many losing jobs and potentially facing poverty they’ve never experienced before.

At the same time, scientists, technocrats and businesses are working feverishly to stem this pandemic and better prepare for the next one. There is little doubt new technology will rise from this epic crisis.

So too might things less tangible.

Americans, by and large, appear to be looking to science to save the day, not to political spin and partisanship. The virus could revive faith in the inarguable forces of biochemistry, deep in the fact-based universe.

On another level, the abrupt disruption of routines that were so long considered by many unalterable — the long daily commute, the business meeting that requires a flight or two, the need to schedule children’s every hour, the go-go-go mentality — opens the possibility of a behavioural reset, for those who can afford it. Millions have stumbled on the ancient simplicity of an afternoon walk and many wonder if there might be a way to reduce some of the noise in their lives, keep the freeways a bit more open and the air a bit more clear.

“People tend to need a big shock to change their behaviour,” said Marlon G. Boarnet, professor and chair of the department of urban planning and spatial analysis at the University of Southern California. In particular, he sees opportunities to fight a slower-moving, potentially far more destructive global disaster: climate change.

“Now we see our day-to-day habits can change more quickly than we thought,” he said. “People have had the opportunity to telecommute. The reality is they didn’t have to go to every conference. And we’re getting a glimpse of what Los Angeles could look like if we could get ahead of our transportation problem.”

He said public officials need to craft policies to make some of the positive changes permanent before old habits return and solidify.

Although many people, from hotel maids to emergency room physicians, cannot do their job online, those who can should consider it, he says. “If we had everybody telecommute a day a week, you would have an incredible air quality improvement.”

Pandemics are famously idiosyncratic in the havoc they cause and the human adaptations that emerge in their wake. An adage among those who study these global infections: “If you’ve seen one pandemic, you’ve seen one pandemic.”

Together, pandemics and epidemics have led to massive advances in public health that allowed cities and civilizations to grow and prosper: germ theory, urban sanitation, vaccination, penicillin, better hygiene, isolation wards and the scientific method, which brought rationality to modern medicine.

Nations and societies rose and fell on the backs of pandemics. The Black Death of bubonic plague that erupted in the 1300s, killing half the population of Europe, dealt the final blows to the feudal order of serfdom, with waves of deadly outbreaks to follow for centuries, shaking faith in the Roman Catholic Church, and some historians suggest, making possible the Renaissance and the Reformation.

But the disruption caused by smaller epidemics, even mere footnotes in history, have also had colossal consequences. Consider how United States obtained the vast midsection of the country that allowed it to expand westward to California and become the most prosperous nation on Earth.

In 1802, Napoleon sent the world’s most greatest army to the Caribbean to put down a slave rebellion and restore French rule in what had been France’s most profitable colony, St. Domingue. But an epidemic of yellow fever devastated his troops, killing an estimated 50,000 and forcing his army to leave in defeat. Without the wealthy island colony to fund his grand plans on the American continent, Napoleon retrenched to Europe to face off with England. St. Domingue became Haiti, the first free black republic in the world, and President Thomas Jefferson bought 828,000 square miles of French territory on the cheap, stretching from New Orleans to the Rocky Mountains to Canada.

So in the great cascade of human events, Kansas City and Denver, and by extension Los Angeles and Seattle and the Silicon Valley, owe a bit of themselves to that long lost ancestor, a pestilence in the Antilles.

Yet a much bigger biological disaster, the influenza pandemic of 1918, which killed anywhere from 20 million to 50 million people globally at the end of World War I, left mere ripples in terms of broader societal change. Some historians dubbed it the “forgotten pandemic” and even the great generation of American writers who lived through it — Hemingway, Faulkner, Fitzgerald — ignored or barely mentioned it in their works.

“Nothing else — no infection, no war, no famine — has ever killed so many in as short a period. And yet it has never inspired awe, not in 1918 and not since,” wrote Alfred W. Crosby in “America’s Forgotten Pandemic.”

How this new virus — SARS-CoV-2 — will bend that human torrent is impossible to know. We’re still crashing down the first rapid.

With modern medicine, and the current data on the virus, no one is predicting the next the Spanish flu or Black Death. But plenty see trouble beyond the death toll and economic fallout.

Many political scientists fear that America’s deep polarisation and divisive president will prevent the nation from rallying around any big policies to save millions from poverty in the event of a recession or to massively reform our healthcare system. No new New Deal seems likely, despite efforts on the left to pass a Green New Deal.

And as the US lets go of the leadership role it had wielded since World War II, and nationalism bubbles up across the planet, it will be harder for countries to cooperate on the big transnational crises: climate change, cybersecurity, terrorism, nuclear weapons proliferation, refugees, every sort of trafficking and the next pandemic. Countries might turn inward, supply chains might contract, the global economy might sputter.

“This is the most global crisis of our lifetimes,” says Ian Bremmer, a political scientist and founder of Eurasia Group, a political risk research and consulting firm. “We desperately need a coordinated response.”