July 16, 1945: An incandescent mushroom cloud in New Mexico heralds the dawn of the nuclear age.
July 20, 1969: Neil Armstrong takes a small step and a giant leap in the dust of the Moon.
February 24, 2022: Russian President Vladimir Putin chews up the world order and 77 years of almost uninterrupted peace in Europe by invading Ukraine, disrupting the supplies of food it produces for many of the planet's eight billion people.
All were watersheds in world history, turning points that will be taught in schools for decades to come. All changed not just lives but also trajectories for mankind, with repercussions felt across continents and for the foreseeable future.
Russia's invasion quickly added Mariupol, Bucha and other Ukrainian names to Europe's long list of cities and towns associated with the abuses of war: Dresden, Srebrenica, the Nazi massacre in France's Oradour-sur-Glane, to name only a few.
And after nearly a half-year of fighting, with tens of thousands of dead and wounded on both sides, massive disruptions to supplies of energy, food and financial stability, the world is no longer as it was.
The air raid sirens that howl with regularity over Ukraine's cities can't be heard in Paris or Berlin, yet generations of Europeans who had grown up knowing only peace have been brutally awakened to both its value and its fragility.
Renewed war in Europe and the need to take sides have also shifted the world's geo-political tectonics and relationships between nations.
Some now barely talk to Russia. Some have banded together. Others, notably in Africa, want to avoid being sucked into the breakdown between Russia and the West. Some don't want to jeopardise the supplies of food, energy, security and income. Russia and Western nations are working — notably, again, in Africa — on fence-sitters, lobbying them to take sides.
The war in Ukraine has held a mirror to mankind, too, reflecting, yet again, its propensity to live on the razor's edge of folly, to take steps back even as it pursues progress.
And there had been progress, with speedy vaccines against the pandemic and deals on climate change, before Putin made it his historical mission to force independent, Western-looking Ukraine at gunpoint back into the Kremlin's orbit, as it had been during Soviet times, when he served as an intelligence officer for the KGB.
With its united stance against the invasion, Nato has found renewed reason for being. Just three years ago, in 2019, the world's biggest military alliance had appeared at risk of slowly sinking into disrepair.
Now Nato is clubbing together increasingly heavy weapons for use by Ukraine on its front lines and relentlessly bombed trenches. It speed-dated Finland and Sweden when those Nordic countries decided that continuing to be non-aligned was too risky in the wake of the Russian invasion.
In Asia, the ripples are consequential, too.
China is scrutinising the Russian campaign for military lessons that could be applied in any eventual invasion of Taiwan. India, China and other energy-hungry Asian nations are boosting the Kremlin's war chest and undercutting Western sanctions by buying growing amounts of Russian oil.
In Ukraine, long before the invasion, many already felt that their country was engaged in a battle of survival against Putin's designs. Since 2014, thousands had already been killed in fighting with Russia-backed separatists in eastern Ukraine.
Soaring prices for food, energy and just about everything — causing pain across continents and largely driven by the war's disruption to supplies — are another change, although perhaps less permanent. High inflation is back as a household term. Some economists warn that "stagflation" — a combination of high inflation and slumping economic growth — could make a comeback, too.
With no end in sight to the war, there are too many ifs and buts to hazard a solid guess. But with each additional day of fighting, the body count and the war's ripples across the globe grow, and peace recedes.