Jim Hoagland is a contributing editor to The Post.

Growing up on a farm in the red clay foothills of the Appalachians did not dispose me to view monarchy as a useful political system. The person who did the most to change that belief was Spain’s King Juan Carlos, who announced last week that he will shortly abdicate his throne.

The announcement triggered wide criticism that the 76-year-old king had waited at least a decade too long. It is impossible to argue with that judgment, since I strongly suspect Juan Carlos has come to agree with it — again.

He once told me that hanging on too long was the mistake monarchs most often make. That he did not take his own advice adds to the unsatisfying nature of Juan Carlos’s legacy after a brilliant start to his reign following the death of dictator Francisco Franco in 1975.

Spain may get lucky once again. On visits to and while studying in Washington, Prince Felipe, 46, who will succeed his father as King Felipe VI, has impressed interlocutors with his command of issues and straightforward manner. He has benefited from the long apprenticeship that being heir to a crown normally brings and has practiced it under the watchful eye of his spirited and shrewd mother, Queen Sofia.

That is, at any rate, how she was once described to me by King Abdullah of Saudi Arabia, another member of the world’s small and exclusive circle of reigning monarchs, who seem to have a surprising amount of interaction. This builds a trust — or at least a sense of common destiny — that foreign ministers issuing joint diplomatic communiques do not enjoy.

Interviews with Abdullah and two of his predecessors, King Faisal and King Fahd, also chipped away at my anti-monarchy instincts. Listening at length to Faisal describe the internal checks and balances that Bedouin society imposed on its rulers led me to conclude that for his country at that time — the early 1970s — monarchy worked to foster an acceptable balance of change and continuity. That was a painful concession for my belief system to make, then and now.

But declared or constitutional monarchies — not the faux versions that Hosni Mubarak in Egypt, Hafez al-Assad in Syria or Moammar Gaddafi in Libya tried to create in their countries — have proved to be at least as stable as other systems tried in the Arab world. But I recognize that is faint praise.

Top-down change in differing degrees has been decreed by rulers in Morocco, Jordan, Oman, Saudi Arabia, the United Arab Emirates, Qatar and Kuwait. On balance, many of these monarchies have helped those countries move forward, if far too slowly, with social, economic and political reform. But even these monarchies risk being overtaken by the global revolutions of cross-border trade, social media and instant communications. Their common challenge is now to adapt more rapidly or die.

European monarchies have adeptly moved with the times. They have become useful as symbols of national unity in divided countries, or dignified national arbiters of political conflicts. They can also become tourist attractions or, in the case of the United Kingdom, all of the above. No sentient being who has met Queen Elizabeth could come away wishing she simply did not exist.

The decision by Juan Carlos to quit playing the game of thrones gives Spain the obligation and opportunity to debate the validity of monarchy in modern Europe.

Juan Carlos was a stabilizing political conciliator amid attempted coups and bitter factional infighting at the start of his reign, helping to build what became a vibrant and prosperous Spanish democracy. But his final years were stained by insensitivity to Spain’s more recent economic woes and family financial shenanigans — by the kind of problems that he seemed to see so clearly when we met in Madrid almost three decades ago.

“He can click off the ages of every monarch in Europe and his or her designated successor, making the point that in too many cases hereditary rulers came to the throne after their prime years,” I wrote in a column in The Post on Sept. 23, 1987. I made clear that he was already thinking of the benefits of going out on the crest of the wave.

“To those who say monarchs should die on their thrones, this pragmatist of a king responds that monarchies could die as well from clinging to outmoded tradition in modern societies.”

The king should have recalled his own words earlier. And kings throughout the world should listen to them in looking at their own futures — or lack thereof.