If the country has no history, it means that very few terrible things like wars and famines, which tend to be written down and passed on in history books, have happened. Thus the nation is happy.
Eduard Gibbon wrote in The Decline and Fall of the Roman Empire: ‘History is, indeed, little more than the register of the crimes, follies, and misfortunes of mankind.’ Thomas Jefferson wrote: ‘Blest is that nation whose silent course of happiness furnishes nothing for history to say.’
The proverb comes on the form of: Happy is the nation that has no history.