In the 19th century, the Scottish writer Thomas Carlyle famously wrote that history is “the biography of great men", popularizing the “Great Man” theory that the course of history is shaped by a select few heroic individuals.

While historians and others continue to debate the accuracy of the Great Man theory of history, there is no question that the course of history is permanently altered by decisive moments in time, where a different result would have produced drastically different outcomes.

As a result, while some of history’s most famous people and events have been permanently etched into the world’s collective imagination, there is a flip side to that coin: Just how differently would history have turned out if certain events never took place?

Charles River Editors’ “What If” alternative history series examines some of these people and events, profiling what happened in reality and how things might have been drastically different otherwise.

Over the last 2,000 years, ambitious men have dreamed of forging vast empires and attaining eternal glory in battle, but of all the conquerors who took steps toward such dreams, none were ever as successful as antiquity’s first great conqueror.

Leaders of the 20th century hoped to rival Napoleon’s accomplishments, while Napoleon aimed to emulate the accomplishments of Julius Caesar. Caesar himself found inspiration in Alexander the Great (356 - 323 BCE), the Macedonian king who managed to stretch an empire from Greece to the Himalayas in Asia by the age of 30. It took less than 15 years for Alexander to conquer much of the known world.

In 323 BCE, Alexander the Great was on top of the world. Never a man to sit on his hands or rest upon his laurels, Alexander began planning his future campaigns, which may have included attempts to subdue the Arabian Peninsula or make another incursion into India. But fate had other plans for the young Macedonian king. Alexander died of still unknown causes at the height of his conquests, when he was still in his early 30s.

Although his empire was quickly divided, his legacy only grew, and Alexander became the stuff of legends even in his own time. Alexander was responsible for establishing 20 cities in his name across the world, most notably Alexandria in Egypt, and he was directly responsible for spreading Ancient Greek culture as far east as modern-day India and other parts of Asia.

For the ancient world, Alexander became the emblem of military greatness and accomplishment. It was reported that many of Rome’s greatest leaders, including Pompey the Great, Augustus, and Caesar himself all visited Alexander’s tomb in Alexandria - a mecca of sorts for antiquity’s other leaders.

Thus, while it could be said that Alexander’s empire continued on through its successors, and that the Hellenistic kingdoms of Macedonia, Seleucia, Pergamon, and Ptolemaic Egypt shaped the course of Western history in the centuries that followed and spread Greek culture throughout the known world, their divisions and animosities also weakened them and made them easier to conquer. One by one, they would fall to Rome.

But what if Alexander had not died in Babylon years before anyone expected to lose him? How would the world have changed had Alexander remained sole king of the Macedonian Empire and lived long enough to designate an heir? Would history eventually have progressed essentially as it did, or would the world look vastly different?

What if Alexander the Great Had Lived?: An Alternative History of the Macedonian King and His Empire profiles Alexander’s life and examines how events may have gone differently if Alexander had survived.