Alternate history, long popular with fiction writers, has also been explored by historians and journalists. Here are some of their intriguing conclusions.

1. What if the South won the Civil War?

Effect: America becomes one nation again… in 1960.

Explanation: In a 1960 article published in Look magazine, author and Civil War buff MacKinlay Kantor envisioned a history in which the Confederate forces won the Civil War in 1863, forcing the despised President Lincoln into exile. The Southern forces annex Washington, DC — renaming it the District of Dixie. The USA (or what’s left of it) moves its capital to Columbus, Ohio — now called Columbia — but can no longer afford to buy Alaska from the Russians. Texas, unhappy with the new arrangement, declares its independence in 1878. Under international pressure, the Southern states gradually abolish slavery. After fighting together in two world wars, the three nations are reunified in 1960 – a century after South Carolina’s secession had led to the Civil War in the first place.

2. What if Charles Lindbergh were elected President in 1940?

Effect: America joins the Nazis.

Explanation: Philip Roth’s bestselling novel, The Plot Against America (2002), gives us an alternate history in which Charles Lindbergh, trans-Atlantic pilot and all-American hero, becomes the Republican presidential candidate in 1940, defeating the incumbent Franklin Roosevelt. President Lindbergh, a white supremacist and anti-Semite, declares martial law, throws his opponents in prison, and allies with Nazi Germany in World War II. Lindbergh is remembered as a national villain – in Roth’s opinion, the reputation he deserves.

3. What if Hitler successfully invaded Russia?

Effect: The Fuhrer is revered in history as a great leader.

Explanation: In Robert Harris’ novel Fatherland (the basis for a 1994 TV movie), Nazi Germany successfully invades Russia in 1942. Learning that Britain has broken the Enigma code, however, the Nazis play it safe and make peace with the west. Through the magic of propaganda, Hitler is revered 20 years later as a beloved leader. It’s an alternate history, of course, but Harris was drawing a parallel with real history: this was Stalin’s Russia with the names changed.

4. What if James Dean had survived his car crash?

Effect: Robert Kennedy survives his assassination attempt.

Explanation: Jack Dann’s 2004 novel The Rebel portrays a history in which film star James Dean survives his fatal car crash in 1955. “I just changed that one thing,” said Dann, who copiously researched his book, making it “as factual as I could… By exploring Dean as he matures, I'm able to cast light on the Dean that we know.” If Dean had survived, Dann suggested, he would have inspired one of his fans, Elvis Presley, to leave rock ’n’ roll and become a serious actor (which was always his ambition). Dean would later become the Democratic Governor of California, consigning his opponent Ronald Reagan to the dustbin of history. In the 1968 presidential election, he would be Robert Kennedy’s running mate, eventually saving him from the assassin’s bullet.

5. What if President Kennedy had survived the assassination attempt?

Effect: Republicans win every election for the next 30 years.

Explanation: The 1963 Kennedy assassination is a popular event of alternate history, inspiring novels, stage plays and short story collections. In an essay in the book What Ifs? of American History (2003), Robert Dallek, a Kennedy biographer, suggested that Kennedy would have successfully pulled out of Vietnam, and that he would be popular enough at the end of his second term to be succeeded by his brother, the Attorney-General Robert Kennedy. Result: no Watergate, more national optimism, and less voter cynicism.

Other writers have been less kind, envisioning that JFK would provoke violent anti-war marches, accidentally start World War III, or continue his affair with Marilyn Monroe (who also survives her early death) for another 30 years.

One of the more unusual theories was written in 1993, on the thirtieth anniversary of President Kennedy’s death. London Daily Express journalist Peter Hitchens wrote a fictitious obituary, in which Kennedy survives, and goes on to become one of America’s most unpopular presidents before finally dying at age 75, mourned by almost nobody. His presidency, the article speculated, would be so disastrous that Democrats wouldn’t occupy the White House for at least another 25 years. Even Bush’s vice-president, Dan Quayle, would be propelled to the presidency after winning a debate against Bill Clinton.

Hitchens didn’t explain how Nixon would avoid the Watergate scandal, or where Quayle would obtain his debating skills. Like everything else in this list, it’s all speculation.

6. What if Christianity missed the West?

Effect: The Enlightenment starts early – and lasts a thousand years.

Explanation: French philosopher Charles Renouvier’s book Uchronie (1876) suggested a history in which Christianity didn’t come to the west through the Roman Empire, due to a small change of events after the reign of Marcus Aurelius. In this history, while the word of Christ still spreads throughout the east, Europe enjoys an extra millennium of classical culture. When Christianity finally goes West, it is absorbed harmlessly into the multi-religious society. Naturally, this view of history was colored by Renouvier’s own worldview: while not strictly an atheist, he was no fan of organized religion.

7. What if The Beatles had broken up in 1966?

Effect: Ronald Reagan is assassinated in 1985 (obviously).

Explanation: Edward Morris’s story "Imagine" (published in the magazine Interzone in 2005) is written as an article by the legendary rock journalist Lester Bangs, which reminisces about Beatlemania – and the Beatles being banned in California after John Lennon controversially states that they are “more popular than Jesus." This leads the Fab Four to disband. Almost 20 years later, Lennon, now an embittered has-been, assassinates Reagan, whose actions – as the conservative Governor of California – had played their part in the break-up.

In this history, while Reagan died 19 years early, other people are granted extended lives. Lennon’s obscurity, of course, ensures that he is not killed by a fan in 1980. Bangs also survives the fate he suffered in reality, where he died of an accidental overdose in 1982, aged 33.

8. What if the Romans won the Battle of the Teutoburg Forest?

Effect: No one would speak English.

Explanation: In What If? (1999), edited by Robert Cowley, historians pondered what would happen if historical events had turned out differently. Many of these were popular questions — What if the Americans lost the Revolutionary War? What if the D-Day invasion had failed in 1944? But an essay by the late Lewis H. Lapham, then editor of Harper’s Magazine, recalled a little-known confrontation in 9 AD between the Roman legions and the Germanic tribes at the Teutoburg Forest. The tribes ambushed and destroyed three Roman legions in this campaign, and the Romans would never again attempt to conquer Germania beyond the Rhine.

Lapham suggested that, if the Romans had won, world history would have been remarkably different, with a “Roman empire preserved from ruin, Christ dying… on an unremembered cross, the nonappearance of the English language, neither the need nor the occasion for a Protestant Reformation… and Kaiser Wilhelm seized by an infatuation with stamps… instead of a passion for cavalry boots.”

9. What if the Protestant Reformation never happened?

Effect: Christianity would continue to rule the world. Science, not so much.

Explanation: Renowned novelist Kingsley Amis entered alternate-history territory in 1976 with his award-winning novel The Alteration. In his imagined history, Henry VIII’s short-lived older brother, Arthur, has a son just before his death. When Henry tries to usurp his nephew’s throne, he is stopped in a papal war. Hence, the Church of England is never founded, the Spanish Armada is never defeated (as Elizabeth I was never born), and Martin Luther reconciles with the Catholic Church, eventually becoming Pope. Naturally, this turns Europe into a vastly different place. By 1976, it is ruled by the Vatican, in the middle of a long-running Christian/Muslim cold war, and technologically regressed, as electricity is banned and scientists are frowned upon.

10. What if Napoleon had kept going?

Effect: Revolution in South America.

Explanation: Probably the first book-length alternate history, Napoleon and the Conquest of the World: 1812-1823 (published in 1836) imagined that Napoleon, rather than freezing in Moscow in 1812, sought out and destroyed the Russian army. One chapter mentions a fantasy novel in which the Emperor suffered a major defeat in the Belgian town of Waterloo. (The idea of a fictitious book, telling the “real” history, was also used by Kingsley Amis in The Alteration.)

But what if Napoleon had won the Battle of Waterloo in 1815? This question was asked in 1907, in an essay contest held by London's Westminster Gazette. The winning essay, by G. M. Trevelyan, suggested that Napoleon would lose interest in expanding his empire, partly because his health was suffering, and partly because the mood in Paris was for peace. England, however, would suffer economically, with many people starving. The poet Lord Byron would lead a popular uprising against the government, which would be suppressed. Byron's execution, of course, would only inspire revolution. Meanwhile, a war of independence would stir in South America. With Napoleon ailing, the French government would nearly cease functioning, attacked from all sides. (The essay ended there – on a cliffhanger.)

11. What if the South had won the US Civil War?

Effect: The Union would be over… forever.

Explanation: The previous list of alternate histories included a historian’s view of what would have happened if the Confederacy had won the Civil War. Of course, the idea has also been popular in fiction. The popular Harry Turtledove, who specializes in alternate history novels, has suggested what might have happened – in 11 volumes (so far). The first novel, How Few Remain (1997), introduced a world where, years after the war, the former USA is divided into two nations: the U.S. and the Confederate States of America. Later volumes were set in the Great War, in which the CSA allies with Britain and France, and the U.S. – still bitter over the two Civil Wars – joins forces with Germany. Using advanced technology, the U.S. is on the winning side. In the South, post-war measures lead to runaway inflation, poverty, and the victory of the violent Freedom party. The newly fascist CSA then plans a Final Solution for the “surplus” black population. In the Second Great War (1941-1944), three American cities and six European cities are destroyed in nuclear attacks. At the end of the war, the U.S. side wins again, and takes control of the CSA.

Sadly, it is too late for the South to rejoin the Union. After all these years of conflict, such a move would fill Congress with some of the USA’s greatest enemies. Instead, the CSA is offered neither independence nor civil rights, but is kept under military rule.

12. What if the Cuban Missile Crisis escalated into a full-scale war?

Effect: The end of nuclear proliferation... except in the U.S.

Explanation: Though usually considered a branch of science fiction, alternate history stories have their own awards, the Sidewise Awards for Alternate History, which have been presented to some renowned novels, including Harry Turtledove’s How Few Remain, mentioned above, and in 1999, Brendan DuBois’ Resurrection Day. This envisions a world in which the U.S. military sabotages President Kennedy’s attempts to negotiate peace during the Cuban Missile Crisis. The United States invades Cuba, making the Crisis escalate into nuclear warfare. The Soviet Union is destroyed, the People’s Republic of China collapses, and a fallout cloud over Asia kills millions of others. Meanwhile, the United States loses New York, Washington DC, San Diego, Miami and other cities. However, all surviving nations renounce their possession of nuclear weapons – with the exception of the USA, now under martial law (as the military had planned all along).

13. What if Marilyn Monroe survived?

Effect: She would win an Oscar – and be brainwashed.

Explanation: Marilyn Monroe’s death in 1962, at age 36, has been pondered by a few writers. In his novel Idlewild (1995), journalist Mark Lawson devised a world where Monroe survived her “suicide attempts,” President Kennedy survived his assassination attempt, and they continued their notorious (if historically unproven) affair for another 30 years. Playwright Douglas Mendin, in a 1992 story for Entertainment Weekly, imagined that Monroe would survive, dedicate herself to serious acting, and win an Oscar in 1965, with no make-up and her hair dyed brown. She would then record a hit song with Frank Sinatra, make bad films, and give up acting in 1980 to look after her drug-addicted twin sons.

Then there was the American supermarket tabloid The Sun. In a 1990 story, they “revealed” that Monroe actually was still alive. According to The Sun, after threatening to reveal an affair with Robert Kennedy, she was drugged, brainwashed and taken to Australia, where she lives the "simple life of a sheep rancher's wife."

14. What if Shakespeare was a renowned historian?

Effect: Due to advanced technology, the Industrial Revolution happens 200 years early.

Explanation: Shakespeare has impressed scholars not only with his literary brilliance, but also with the historical detail of his plays. He did get a few things wrong, however—such as having a clock strike in Julius Caesar, 1500 years before such clocks were invented. The acclaimed 1974 novel A Midsummer Tempest, by popular science fiction and fantasy author Poul Andersen, was set in a world where Shakespeare’s plays are utterly accurate, and the Bard is renowned not as a creative genius, but as a great chronicler of history. Hence, fairies and other magical beings exist on this world, and the clockwork technology of Ancient Rome advanced to the stage where, in the age of Cromwell, steam trains are already running through England.

15. What if Woodrow Wilson had never been US president?

Effect: World War II would have been avoided.

Explanation: In Gore Vidal’s 1995 novel, The Smithsonian Institution, the great political scribe made one of his rare entries into science fiction. In the book, a teenage math genius is mysteriously summoned to the Smithsonian Institution in 1939, where he glimpses the upcoming World War II. Determined to prevent it, he goes back in history to seek its origins. At one stage, he concludes that the fault lay in President Woodrow Wilson’s vision for the League of Nations. Well-meaning as the organization was, Vidal blames it for causing Germany’s struggles in the 1920s, paving the way for the rise of Hitler.

16. What if Frank Sinatra was never born?

Effect: Nuclear devastation.

Explanation: In "Road to the Multiverse," a 2009 episode of Family Guy, Stewie and Brian find themselves hopping between universes. They find themselves in a Disney universe, where everything is sweet and wholesome (as long as you’re not Jewish); a universe inhabited only by a guy in the distance who gives out compliments; a universe where Christianity never existed, meaning that the Dark Ages didn’t happen; and a universe in which the positions of dogs and people are reversed. One of the most intriguing was a universe where Sinatra was never born, and is therefore unable to use his influence to get President Kennedy elected in 1960. Instead, Nixon was elected, and “totally botched the Cuban Missile Crisis, causing World War III.” This caused devastation all around them. Lee Harvey Oswald didn’t shoot Kennedy, but shot Mayor McCheese instead. (That bit was never explained.)

17. What if Franklin Roosevelt was assassinated in 1933?

Effect: Colonization of the moon, Venus, and Mars by 1962.

Explanation: Any reality envisioned by Philip K. Dick was bound to be fascinating. His 1962 novel The Man in the High Castle, which established him as a top science fiction writer, is set in a world where the Axis powers win World War II in 1947 and divide most of the world between them. This happens because, in this world, Giuseppe Zangara’s attempted assassination of President-elect Roosevelt is successful. Under the government of John Nance Garner (who would have been Roosevelt’s VP), and later the Republican candidate John W. Bricker, the U.S. doesn’t prevail against the Great Depression, and maintains an isolationist policy in World War II, leading to a weak and ineffectual military. In the America of 1962, slavery is legal once again, and the few surviving Jews hide out under assumed names. However, the Nazis have the hydrogen bomb, which also gives them the technology to fuel super-fast air travel and colonize space. This book, with its historical commentary, made many critics take sci-fi far more seriously, showing that it was more than just alien invasions and spaceships. Unlike many of Dick's later works, it has yet to be turned in to a movie, though a SyFy TV series is currently in planning stages, produced by Sir Ridley Scott.

18. What if Germany had invaded Britain by sea?

Effect: World War II might have ended earlier—but Hitler would still have lost.

Explanation: After capturing France, Nazi Germany planned to invade Britain with Operation Sea Lion, in an air and naval attack across the English Channel. The plan was shelved in 1940, but some 30 years later, the Royal Military Academy of Sandhurst started a war-games module, set in a world where Sea Lion had happened. (Military academies, in their war-games, often speculate about how different strategies might have changed history.) According to the module, the Germans would not have been able to withstand the might of the British Home Guard and the RAF—and as the Royal Navy had superiority in the English Channel, they would not have been able to escape. It would have severely weakened the German army, and hastened the end of the war.

19. What if Martin Scorsese had directed Pretty Woman?

Effect: One of America’s favorite rom-coms of the 1990s would have been a gritty tragedy.

Explanation: The British movie magazine Empire joined in the counterfactuals game in 2003 by suggesting some possible stories from recent Hollywood history. Somehow, we’re not convinced that they took the job seriously, as they pondered worlds where The Godfather had flopped (forcing Francis Ford Coppola’s return to directing porn movies and Al Pacino’s return to his job as a furniture removalist), Sean Connery was gay (so that, rather than James Bond, he wins stardom in camp British comedies), and, most cruelly, Keanu Reeves was born ugly (“He would have starved to death at a very young age”), among other twisted scenarios. Perhaps the most intriguing was the reality in which Martin Scorsese, rather than Garry Marshall, directed Pretty Woman (1990), the rom-com that turned Julia Roberts into a star. As imagined by Empire scribe Richard Luck, Scorsese would retitle the film The Happy Hooker, and it would become a hard-hitting study of life on the streets. It would end not with the prostitute (Roberts) and her wealthy client (Richard Gere) living happily ever after, but with her dying of a heroin overdose while he drives into the sunset, cackling maniacally.