Well, no nation actually had a circumcision "policy", though it's true that the US, Australia, NZ and Canada went through periods where most boys' foreskins were pretty much automatically removed at birth. As they used to say, the biggest threat to a newborn's foreskin is the English language. All these countries took their cues from the early experiments with medical circumcision by the UK and US in the late 1800's. Whereas in England the fad was largely confined to the upper and upper-middle classes (and oddly didn't cross borders much into Scotland and Wales), in the colonies and former colonies the fad took solid hold in the early 1900s. Without Britain's rigid class distinctions, circumcision was equally and enthusiastically endorsed and applied by the medical profession across most socioeconomic lines -- at least those that could pay and those that didn't outright object.
In England, the rate never got much above about 35%, limited to the elite. A friend who attended Oxford University in the early 1960s said he never saw a foreskin in his college or from other colleges the whole time he was a student. It was practically unthinkable in the Oxbridge crowd before the end of WWII to not have your son circumcised. All this changed with the advent of the NHS in July 1948. Physicians' attitudes toward circumcision soured quickly and even the wealthiest Britons eventually took part in the scheme, so by the early 1950's England's circumcision rate was down near the traditional continental rate of 1% or so. The real nail in the coffin was an article in the British Medical Journal (Christmas 1949) by a highly respected paediatrician, Douglas Gairdner, DM.
Australia and NZ had probably the highest nonreligious circ rates during the 20th century, around 95-98%. This actually began around World War I and didn't start to come down until around 1970, so it is rare to find an intact Aussie or Kiwi guy over 40. New Zealand actually led Australia in this change by about 10 or 15 years, possibly owing to its closer ties with Britain. NZ didn't have its own medical society until the early 1960s; prior to that, it was the NZ chapter of the British Medical Association. As such, NZ docs were well aware of the British abandonment of infant circumcision, and this likely influenced attitudes, but it wasn't really until single-payer health came to NZ around in the late 1960s that the rate there began to plunge.
Canada, as a Commonwealth country, embraced infant circumcision, though not as aggressively as Oz and NZ. While Australia was busy snipping nearly every boy, Canadians never got much above about 80%, owing in part to the greater rural and farming population. This started to change in the late 60's and early 1970's as numerous British-trained doctors questioned the need for circumcision, just like in Australia. But the real drop came with the start of single-payer health systems province-by-province. The ones that dropped circumcision from coverage early, like Alberta, BC, and the Maritimes, saw rapid declines in the early 1980s. Ontario dropped coverage much later, but has also seen steep declines in infant circumcision.
The story in the US is, predictably, more driven by private enterprise than by social trends or commonwealth practices. The infant circumcision rate started to rise in the early 20th century, but didn't really take off until the big push for standardized hospital maternity wards after WWI. Between the world wars the US rate rose from about 25% to about 60%. After WWII there was an economic boomlet and companies were fiercely competitive for workers. However, the US maintained strict wage controls, so private industry turned to offering generous insurance benefits as lures -- fueled by an important IRS ruling that health insurance benefits were not taxable income to employees. These big private insurance schemes and later HMOs, today largely unsupportable, are still the cornerstone of the ailing US healthcare system. Male infant circumcision was added to virtually every insurance program by the early 1950s and doctors liberally took advantage of the guaranteed reimbursement.
Circumcision got one of its biggest pushes the year after WWII with the publication of Baby and Child Care by paediatrician Benjamin McLane Spock. His book became the bible of child-rearing in the 1950s and in it, he offered a circular-logic endorsement of infant circumcision: he suggested that circumcision was a good idea, particularly if most of the boys in the neighborhood were also circumcised, so a boy grows up feeling "regular". Of course, the opposite could have been argued if most of the boys in the neighborhood were not circumcised, but the end result was that just about every parent went along with circumcision. No one wanted their son to dwell on being "different" or, heaven forbid, to become a "homo". Plus, circumcision was rapidly becoming "free" with insurance.
Spock also revealed his general ignorance of intact anatomy by telling parents that if they did not opt for circumcision, they must systematically pull back their son's foreskin every day from birth for careful cleaning of the glans. He noted this may be difficult, and painful, at first, but must be done. In this way, many intact boys suffered painful adhesions and infections and ultimately needed to be circumcised, scaring many more parents into having their newborn sons circumcised. No matter that this wasn't happening in Europe, South America or Asia, where parents left their sons alone.
Significantly, Dr Spock later regretted his advice. He wrote in 1989 that he eventually came to believe there were no medical or hygienic benefits to infant circumcision, and his view was that routine circumcision of males is traumatic, painful, and of questionable value. He said he would not have any son of his circumcised, a sentiment shared by a high percentage of US doctors.
US circumcision reached its peak around the time of Kennedy's election, at probably around 90%. In more than a few communities it was 100%; in some rural areas, less. Blacks initially lagged behind, but eventually caught up and today have slightly higher overall circumcision rates than whites.
Meanwhile there were a few dissenters in print. One was a writer named Joseph Lewis, who wrote a 1949 book called "In the Name of Humanity". It was a solid treatise against what he saw (correctly) as the coming huge run-up in the infant circumcision rate. Another was a landmark article in the Journal of the American Medical Association (JAMA) by Air Force Captain Noel Preston in September 1970. Its 3-sentence conclusion stated that routine infant circumcision was unnecessary and contraindicated. Shortly thereafter, in 1971, the American Academy of Pediatrics (AAP) issued its first statement on circumcision, stating "There are no valid medical indications for circumcision in the neonatal period."
This was the start of American doctors and parents reëvaluating the need for automatic circumcision of boys at birth. The US medical community remained unpersuaded by worldwide medical opinion & practices regarding infant circumcision, but still has never officially endorsed the practice. With easier access to information showing the US has obtained no health advantages at all from mass circumcision, more and more parents and doctors are not bothering with the procedure. The US rate is now estimated to be somewhat under 60%, similar to at the end of WWII, down from about 80% when Reagan took office. But there will be no plunge similar to in Britain or the Commonwealth countries until US health insurance drops automatic coverage. Non-religious circumcision has always clearly been more an economic issue than a health or cultural issue.
By the way, strutter2, you're not alone in not knowing that probably every American guy you've met is circumcised. Most Britons and other Europeans are quite surprised when they learn this, since it seems at odds with prevailing views of the USA.