Day 01Four Heartbeats Under the Iron CurtainBerlin Airlift · Cuban Crisis · Berlin Wall · Soviet Collapse
Day 02Four Locks That Cracked Open the 20th CenturyMidway · Stalingrad · D-Day · The Bomb
Day 03From Humen to the Red Building — Eighty YearsOpium War · Hundred Days · Xinhai · May Fourth
Day 04From Jingxi Hotel to Taobao: Four Turns Through Narrow Gates3rd Plenum · Southern Tour · WTO · Internet Rise
Day 05From Uraga Bay to Toyota: Japan's Four Catch-Up GamblesBlack Ships · Meiji Restoration · Russo-Japanese War · Postwar Miracle
Day 06"All Men Are Created Equal" — and One Deleted SentenceDeclaration · Constitution · Civil War · Reconstruction
Day 07From a Sliver of Germanium to a Phone: Four Fissions of the ChipTransistor · Traitorous Eight · Moore's Law · ARM/RISC-V
Day 08From the Garage to the Palm: Four Leaps of the PCApple I · IBM PC · Windows 95 · iPhone
Day 09Beginning With Half a Word: The Internet's Four ConnectionsARPANET · WWW · Netscape IPO · PageRank
Day 10Machines That Think: AI's Four SummersDartmouth · AI Winters · AlphaGo · ChatGPT
Day 11Racing Death: Four Forks in Modern MedicinePenicillin · Double Helix · Human Genome · mRNA
Day 12From a Beep to a Rocket That Lands ItselfSputnik · Apollo 11 · Hubble · SpaceX
Day 13Ignition and Blackout: Four Fault Lines of Modern EnergyOil Shock · Chernobyl · Shale · Solar
Day 14The Price of Trust: Four Collapses of Monetary OrderWeimar · Nixon Shock · Asian Crisis · Bitcoin
Day 15How Giants Fall: The Unmaking of Four EmpiresRome · Ottomans · Britain · USSR
Day 16Unshackling Energy: Four Waves That Built the Modern WorldSteam · Railways · Electricity · Digital
Day 17Four Fault Lines: The Choices That Shaped the Modern Middle EastIsrael · Iran · Gulf War · Arab Spring
Day 18A Continent's Rise and Fall: Who Gets to Write Africa's FateBerlin Conference · Independence · Rwanda · Leapfrog Rising
Day 19Continent of the Pendulum: Latin America Between Revolution and CollapseBolivia 1952 · Cuban Revolution 1959 · Chile coup 1973 · Argentina 2001 crisis
Day 20Seeing the Invisible Risk: Four Moments Humanity Learned to Read the ClimateTambora 1815 · London smog 1952 · IPCC reports · Paris Agreement 2015
Day 21Choices at the Cliff's Edge: Four Leaders Who Refused the Easy RoadLincoln & the Civil War · Churchill at war · FDR & the New Deal · Mandela's reconciliation
Day 22Settling Accounts with the Past: How Four Societies Decided What to Remember and Whom to ForgiveBrandt's Warsaw kneel · South Africa's TRC · Argentina's junta trials · China's 1981 history resolution
Day 23The Market-Makers: Four Firms That Rewrote the RulesWedgwood's brand · Rockefeller's scale · Sony's innovation · oil shock & Toyota
Day 24Building a World with Reason: The Four Faces of the EnlightenmentNewton & the Royal Society · Voltaire · founding America · the Enlightenment's dark side
Day 25Four Wagers to Feed the World: From the Heavy Plow to Synthetic Nitrogenthe heavy plow & three-field system · Haber–Bosch · the Green Revolution · Golden Rice
Day 26Four Accelerations That Compressed Time and Space: From Rails to Self-Drivingsteam locomotive 1825 · the DC-3 · China's high-speed rail · self-driving cars
Day 27Whom the City Takes In, and Whom It Casts OffBooth's poverty maps · Moses vs. Jacobs · Shenzhen & the hukou · the siphon effect
Day 28You Push the Door Open, and It Swings Back: Four ThresholdsTennessee's deciding vote · Rosie the Riveter · The Feminine Mystique · Bandaranaike
Day 29After the Rupture: Four Turning Points, Four Choicesthe trial of Socrates · the Statute of Labourers · the Florence dome · Asilomar 1975
Day 30Germs Don't Decide: Four Plagues, Four Human ForksPlague of Athens · Ragusa invents quarantine · smallpox at Tenochtitlan · Philadelphia 1918
Day 31The Imperial Ledger of Four Cropsthe Banda massacre · the Barbados Slave Code · the potato & the Irish Famine · London coffeehouses
Day 32Four Times the Sea Became a Roadthe monsoon network · the end of the treasure fleets · the Zong & marine insurance · the container & ISO 668
Day 33Four Ways a Promise Became MoneyLydian coinage & the stamp · the Chengdu reserve · double-entry & the Medici · Bretton Woods & the Triffin dilemma
Day 34Four Times Words Got CheaperUruk tablets & Enheduanna · Talas & paper moving west · Gutenberg's punch-and-matrix · the Index & the 1695 lapse
Day 35Climate Only Sends the Bill; Institutions Decide Who Paysthe Green Sahara closes · Norse Greenland · Chongzhen's post stations & surtaxes · the 1876 El Niño
Day 36The Map of Cloth Was Never Drawn by the Marketsilk as Tang military pay · the cotton famine and Egypt's debt · why the jenny paid in Britain · quotas that built Dhaka
Day 37The Shape of a Human Tide Is Cut by a Documentthe Alhambra Decree · Batavia's Kapitan system · the quarter-acre clause · the 1951 definition
Day 38The Civilization Didn't Vanish — Its Readers DidIndus weights · Great Zimbabwe's stratigraphy · Hōkūleʻa re-runs the route · the khipus burned in 1583
Day 39The Life-Saving Part Already Existed — It Was Stuck Elsewherethe Chamberlen forceps secret · Ether Day 1846 · Wu Lien-teh in Manchuria · deinstitutionalization 1963
Day 40Everything You Do Without Thinking, Someone Once Decidedthe Amiens work-bell 1355 · the invention of the corridor · the stews closed 1546 · the fork reaches England
Day 41The People Left Out of the Count Understood the Rules Bestthe pirate articles 1721 · the Settlement Act 1662 · Bamberg's witch trials 1626 · Ge Cheng and the Suzhou weavers 1601
Day 42A Disaster Does Not Happen on the Day It HappensQuebec Bridge 1907 · Titanic 1912 · Challenger 1986 · Chernobyl 1986
Day 43A Map Shows Who Could Afford to Measure the WorldPtolemy c. 150 · the Great Arc 1802 · the race to the Pole 1911 · Tharp's rift 1952
Day 44Once Sound Could Be Measured, It Had an OwnerZhu Zaiyu's ratio 1584 · the bells melted 1793 · three minutes in Calcutta 1902 · City Noise 1930
Day 45What Decides a War Is Usually Not the Fightingthe Hansan supply lane 1592 · rations refused 1904 · the Lieber Code 1863 · the can before the opener 1810
Day 46Law Is Not Deduced From Justice. It Grows Out of Trouble.a stele no judge cited · the Digest cuts 95% in 533 · the jury fills the ordeal's vacuum 1219 · Grotius briefs for stolen cargo 1609
Day 47The Decisive Changes in Education Were Never About What Gets Taughtnames sealed and papers recopied 992–1015 · scholars' privileges and the walkout 1155 · absence fined by the day 1763 · reading without writing 1686
Day 48The History of the Family Is Written in Ledgers Kept to Manage PeopleTametsi requires witnesses 1563 · fewer births before contraception · mean household 4.75, 1574–1821 · the age line before the register 1833
Day 49Religion Turns on Who Is Allowed to Supply Itthe theses hit a debt-service cash flow 1517 · evangelical petitions cast the deciding votes 1786 · Connecticut bans itinerancy 1742 · the break came around 1963
Day 50Play Became an Industry When Someone Started Timing and Scheduling Itfines cast into statues of Zeus, 388 BCE · the split over "hacking" 1863 · a broadcast staged to sell radios 1921 · one timing contract and the quartz crisis 1964
Day 51Empires Are Assembled from Contracts and Ledgers — and So Is Their Undoinga secret pact turns a firm into a state 1757 · rubber quotas & severed hands 1890s · a pinch of salt 1930 · a border drawn in five weeks 1947
Day 52Cities Are Not Built. They Are Kept Fed.a siege that cut the aqueducts 537 · submission traded for self-rule 1183 · the calculation that doubled a pipe 1858 · an expressway never built 1969
Day 53Your Most Private Feelings All Have an Invention Dateindicted for knowing one another 166 · love judged out of marriage, consent written into it 1174 · a funeral train of 1,700 miles 1865 · inventing a legal word for private life 1890
Day 54Science Was Not Driven by Geniuses. It Was Driven by a Few Boring Rules.a journal that takes nobody’s word for it 1665 · a nomenclature where the name is the composition 1787 · apprenticeship turned into a line 1826 · who defines what is worth doing 1945
Day 55How Fast News Travels Is How Far Power Reachesa revolt report six days late 755 · the telegraph patent Congress refused 1844 · the two thousand volts that burned the cable 1858 · the cut that deleted meaning 1948
Day 56The Body Is Society’s Most Honest Ledger — and Its Handiest Toola conscription ruler measures poverty 1829 · the machine yarn that undercut bound feet 1895–1928 · an actuarial table becomes a nation’s morning drill 1928 · twenty-six days in a federal building 1977
Day 57The Past Does Not Survive on Its Own. Someone Decides What Is Kept.seven years of letting the defeated speak 1958 · thirty-two years for a few lines 1965 · a black wall of only names 1982 · 174,000 informant reports handed back 1990