Oh, brother

Prince Harry's memoir is called Spare. Traditionally, the eldest son inherits everything from his parents. The younger brother is a spare and gets nothing.

This relationship can create jealousy and hatred. For the princes, it became a public row. But in history, sibling rivalry has led to war and the fall of empires.

The first murder. In the Bible, Adam and Eve's eldest son Cain grew jealous of his brother Abel. God accepted a sacrifice from Abel but refused Cain's gift. So Cain killed Abel.

Death in Rome. Twin brothers Romulus and Remus fought over where to build Rome. Remus was killed when he ignored the gods. For Romans, this origin myth stressed the importance of unity and divine power.

Divided spoils. According to one chronicler¹, William the Conqueror's three sons fell out because William and Henry tipped a chamber pot over Robert's head. He never forgave them.

When William I died, he split his kingdom between them, sparking a civil warA war between people from the same country. . William II was killed in a suspicious hunting accident.² And Henry threw Robert in prison.

Brothers in arms. In 15th Century England, the rivalry between three princes tore apart the House of York.

Historians disagree about who killed who. But Shakespeare made the youngest into the villain. In his play³, Richard III drowns his brother George in wine and murders Edward's sons in the Tower.

Culture clash. In 1532, 169 Spanish soldiers invaded the IncaA native South American people who lived in the Andes before the Spanish conquest. Empire. It had powerful armies. But it was divided by a war between two brothers, Atahualpa and Huascar.

The Spanish took Huascar's side. After Atahualpa killed his brother, the Spanish executed him and took control.

The psychologist Alfred Adler argued that siblings compete for "significance". The rivalry shapes history. But others argue brotherly love holds society together.

Yes: History is the story of men dividing their land and wealth between their sons. No heir was a problem. One son secured the family's future. Two or more meant trouble.

No: There is so much more to history. For example, better technology helped the Spanish defeat the Incas. And new diseases from Europe killed more people than the Spanish.

Or... Sometimes. "The heir and the spare" survives in the British royal family, but the rest of society has changed. Power and positions are no longer inherited but given based on ability and merit.