September 3

Octavian's admiral Agrippa defeats Sextus Pompey at the Battle of Naulochus, ending organized opposition to the Second Triumvirate.

Agrippa's naval forces decisively defeated the fleet of Sextus Pompey, son of the famous Roman general Pompey the Great, off the coast of Sicily. The victory eliminated the last significant military threat to the Second Triumvirate's authority and cleared the way for the eventual showdown between Octavian and Mark Antony that would determine the future ruler of Rome.

San Marino is traditionally founded by Saint Marinus, becoming what is now the world's oldest surviving republic.

According to tradition, a Christian stonemason named Marinus fled religious persecution and founded a small community atop Mount Titano in present-day Italy, which gradually developed into the independent republic that survives today. San Marino's continuous existence as a sovereign state, surrounded entirely by Italian territory, makes it one of the oldest and smallest republics still functioning in the modern world.

Richard the Lionheart is crowned King of England at Westminster Abbey.

Following the death of his father Henry II, Richard was formally crowned King of England in a lavish ceremony at Westminster Abbey, though he would spend only a small fraction of his decade-long reign actually residing in England, focusing instead on Crusading campaigns abroad. His coronation is also notoriously remembered for anti-Jewish violence that erupted in London during the celebrations.

Mamluk forces achieve their first decisive victory over the Mongols at the Battle of Ain Jalut in Palestine.

Mamluk forces from Egypt inflicted a crucial defeat on the previously unstoppable Mongol army in Palestine, marking the first major military setback the Mongols had suffered in their westward expansion. The victory halted further Mongol advances into Egypt and the broader Islamic heartland, preserving Mamluk power in the region for centuries to come.

The Battle of Worcester, the last major engagement of the Wars of the Three Kingdoms, ends in Parliamentarian victory.

Oliver Cromwell's Parliamentarian New Model Army decisively defeated the Royalist forces of Charles II at Worcester, effectively ending the prolonged series of conflicts collectively known as the Wars of the Three Kingdoms. Charles II narrowly escaped capture, famously hiding in an oak tree before eventually fleeing into exile in Europe, not returning to claim the throne until the Restoration nine years later.

The American Revolutionary War formally concludes with the signing of the Treaty of Paris.

Negotiated in Paris between American and British representatives, the treaty formally recognized the independence of the United States and established the young nation's boundaries, bringing an official end to the Revolutionary War. The agreement also addressed issues including fishing rights, debts, and the treatment of Loyalists, shaping the diplomatic relationship between the two nations going forward.

Frederick Douglass escapes from slavery, later becoming a leading abolitionist and orator.

Disguised in a sailor's uniform and carrying borrowed identification papers, Douglass boarded a train in Baltimore and made his way north to freedom in New York City, a daring escape from slavery he later described in his influential autobiographies. He went on to become one of the most prominent abolitionist speakers and writers of the nineteenth century, advocating tirelessly for emancipation and civil rights.

Britain, France, Australia, and New Zealand declare war on Germany following the invasion of Poland.

Honoring their treaty commitments to Poland after Germany's invasion two days earlier, Britain, France, and several Commonwealth nations including Australia and New Zealand formally declared war on Germany. The declarations marked the definitive start of a global conflict that would eventually draw in dozens of nations and become the deadliest war in human history.

A three-day victory celebration begins across China marking the end of the war against Japan.

Following Japan's formal surrender the previous day, celebrations erupted across Chinese cities marking the end of nearly eight years of brutal war against Japanese occupation, a conflict that had caused millions of Chinese casualties. The victory also set the stage for the resumption of China's civil war between Nationalist and Communist forces, who had maintained an uneasy alliance against Japan.

Sweden switches overnight from driving on the left side of the road to the right, an event known as Dagen H.

In a remarkably well-organized single-night transition, Sweden switched its entire road traffic system from driving on the left side of the road to the right, aligning with its Scandinavian neighbors. The change, known as Dagen H, or H Day, required replacing road signs, adjusting bus doors, and extensive public information campaigns, and it occurred with far fewer traffic accidents than many had feared.