On July 17, Japan¡¯s parliament enacted the first major substantive revision to the Imperial House Law in nearly eight decades.

To address a shrinking monarchy, the Diet created a legal pathway for the imperial family to adopt unmarried males from eleven former branch families ¡ª lineages that surrendered their royal status during the Allied Occupation in 1947. The law also allows princesses to retain imperial status after marrying commoners, though their children remain excluded from the succession line. Meanwhile, Emperor Naruhito¡¯s only child, Princess Aiko, remains strictly barred from succeeding her father.

Proponents framed the vote as a defense of ¡°timeless tradition.¡± As a historian from overseas living in Japan, I have no stake in whether Princess Aiko or a distant male-line descendant ultimately ascends the throne. But I do have a stake in historical accuracy. And the historical record is clear: The absolute prohibition on female monarchs is not timeless. It is a surprisingly modern invention.