Frankel, shown here winning the 2011 Queen Elizabeth II Stakes, is the best British racehorse ever by some measures. (Carl Court/Getty Images)

Racing fans in the U.S. have reason to believe that the thoroughbred species is in decline. This year’s anticlimactic Triple Crown series was the fifth in a row in which the nation’s 3-year-olds were subpar by historical standards. When the Breeders’ Cup is run next month, the year-end championship events likely won’t produce any winners considered superstars.

But this relative weakness isn’t a thoroughbred phenomenon; it is an American phenomenon. In many parts of the racing world — Britain, Japan and Australia, for example — the quality of thoroughbreds appears to be better than ever. Many extraordinary runners have competed in Britain over the past few years, notably the brilliant colt Frankel. The 4-year-old has regularly scored runaway victories against top-class competition, and he will attempt to complete a perfect 14-for-14 career when he runs in the Champion Stakes at Ascot on Saturday. Respected British racing experts already rate him as the greatest thoroughbred in history.

The decline of the U.S. and the ascendancy of Britain is a slow-developing trend that has spanned decades. Racing in this country peaked in the 1970s. Any short list of the best American thoroughbreds would be dominated by runners from that decade, notably Secretariat, Seattle Slew, Affirmed, Spectacular Bid, Forego and Ruffian. Yet since 2000, this country has scarcely produced a horse who could be ranked with such elite company. I could name only one: Ghostzapper, the horse of the year in 2004.

By contrast, Sea the Stars was judged one of Europe’s all-time best runners after capturing the Epsom Derby and Prix de l’Arc de Triomphe in 2009. The extraordinary mare Goldikova won 14 Grade I stakes, including three straight victories over males in the Breeders’ Cup Mile from 2008 to 2010. Harbinger was lauded for delivering one of the most brilliant performances by a British horse when he beat a stellar field by 11 lengths in the 2010 King George VI and Queen Elizabeth Stakes. And then Frankel came along to eclipse them all.

The colt won the 2,000 Guineas, the first of the English 3-year-old classics, with a display of raw speed that, for Americans, might have evoked memories of Seattle Slew in his prime. He sped off to a 15-length lead and buried the field with a performance that was as visually impressive as a racehorse can deliver.

Runaway wins can sometimes be deceptive, but Frankel has verified his quality by the margins with which he defeats rivals of unquestionable high quality. Last year he had a showdown with Canford Cliffs — who had won five straight Grade I stakes and had defeated the mighty Goldikova in his previous start — and trounced his rival by five lengths. In June he annihilated solid Grade I competition in the Queen Anne Stakes at Ascot by 11 lengths.

The venerable company Timeform has assigned numerical ratings to the performances of European thoroughbreds since 1948, and it gave Frankel’s win in the Queen Anne a rating of 147, eclipsing the 145 earned by Sea-Bird, the legendary runner in the 1960s. By Timeform’s assessment, Frankel is the best ever.

What accounts for the proliferation of great horses in England and their shortage in America? One factor may be the U.S.’s liberal use of drugs that are banned in almost every other racing jurisdiction. Horses win major races with the help of medications, go to stud, pass on their infirmities to their offspring and weaken the breed. The theory appears to be confirmed by the high attrition rate of colts in the Triple Crown series.

But the indisputable explanation for Britain’s ascendancy is its possession of superior thoroughbred genes. The U.S. owed its former supremacy to the same factor. In the years during and after World War II, top European thoroughbred stock was exported to the U.S. and transformed the breed on this side of the Atlantic. Nasrullah arrived in the U.S. in 1950 and by the 1970s his mark was everywhere. He was an ancestor of eight Kentucky Derby winners in the 1970s, including Secretariat, Seattle Slew and Spectacular Bid.

Yet U. S. racing was at its peak, the balance of power slowly began to shift. Britain’s Robert Sangster and his associates recognized that the Maryland-based Northern Dancer was as prepotent a stallion as Nasrullah had been. Europeans began to dominate U.S. yearling sales to acquire offspring of Northern Dancer and his sons, such as the brilliant Danzig. They bred their mares to these same stallions. As the prices for yearlings and stud fees reached astronomical levels, American breeders didn’t hesitate to sell these precious pedigrees.

Sangster bred his mare Fairy Bridge to Northern Dancer in 1980 and the mating produced Sadler’s Wells, who went on to became the best sire in the world and the greatest in European history, begetting more than 320 stakes winners. He sired Epsom Derby winner Galileo, now the most valuable stallion in the world, who in turn sired Frankel.

Prince Khalid Abdullah bred a mare to Danzig, and the mating produced Danehill, who became the most prolific sire of stakes winners in history by shuttling between Britain and Australia. His son Dansili begat Harbinger, who in 2010 earned a 140 Timeform rating (the ninth-best ever.)

Thanks to its acquisition of the best U.S. genes in the 1970s and 1980s, Britain now has the pedigree power to produce the best horses in the world. American racing fans will surely look on these developments with regret, wishing that we had could be thrilling to the exploits of a superhorse like Frankel.