When Henry VII died in 1509, having been preceded in death by his eldest son Arthur, the English throne passed to his second-oldest son, Henry, who is known to history as Henry VIII. But there was Henry's older sister, Margaret, who was skipped over because of male primogeniture in favor of her younger brother.
What would have changed in the flow of history if Margaret had been allowed to take the throne in her own right as Queen of England instead of Queen of Scotland by marriage?