When the inhabitants of the United Kingdom and television audiences across the world celebrate Elizabeth II¡¯s Platinum Jubilee this weekend, one telling secret of her popularity is likely to be overlooked. As her most authoritative recent biographer, Robert Hardman puts it, ¡°the queen genuinely enjoys being queen.¡±

That is not the dominant narrative about the ¡°Firm.¡± Watch the Netflix drama series ¡°The Crown¡± (regarded by millions of viewers as historical fact, rather than truth mixed with surmise and exaggeration), and you see a family in which personal feelings are forever sacrificed to the claims of duty. It presents a joyless, careworn monarch forced to overcome crisis after crisis over her seven-decade reign.

If modern monarchy is such a vale of tears, why didn¡¯t the queen hand over the reins to her eldest son and heir, Prince Charles, long ago?

The answer lies, in part, in her religious sense of vocation. The queen also has bitter memories of her uncle Edward VIII¡¯s abdication, which placed the crown on the unwilling head of her shy, stuttering father.

But mainly, Elizabeth likes doing the job. With some justice, she thinks she is good at it.

Others agree. In 2015, when President Barack Obama was invited to deliver a memorial address for former Israeli President Shimon Peres, he compared him to ¡°giants of the 20th century I have had the honor to meet.¡± One of those two giants, unsurprisingly, was Nelson Mandela, but the other was the queen.

The giants were ¡°leaders who have seen so much, whose lives span such momentous epochs, that they find no need to posture or traffic in what¡¯s popular at the moment. People who speak with depth and knowledge, not in sound bites,¡± said the former president. And respect for the queen is one subject on which Obama, Donald Trump and 11 other U.S. presidents who have met her can agree.

Despite the recent loss of her husband and helpmate, Prince Philip, the queen is visibly enjoying her return to public life, even if at 96 years of age most exerting duties will now fall to Charles, the Prince of Wales.

But if the royals are a ¡°firm,¡± what would a fair assessment of its performance look like?

The main achievement is in managing Britain¡¯s decline from the height of its global power. The queen¡¯s predecessors presided over an empire, which reached its territorial zenith at the time of her birth. She came to the throne five years after Indian independence. The loss of this ¡°jewel in the Crown¡± was followed by independence for most of Britain¡¯s former colonies.

While Britain¡¯s status was dramatically changing abroad, it always seemed the same at home with the...