Circumcision is a religious ritual in certain faiths, including Judaism and Islam. Historically, this has been an important marker of identity, said Shaye Cohen, a Jewish studies professor at Harvard who has written on cultural interpretations of circumcision. "Many Jews see circumcision as an essential marker of Jewishness," he said.

In the book of Genesis, God commands Abraham to become circumcised, and to have all of his sons and members of his household circumcised as well. This is part of his covenant with the Jews; God warns that "any uncircumcised male, who has not been circumcised in the flesh, will be cut off from his people."

"Even if Jews don’t observe anything else, they see [rejecting circumcision] as akin to rejecting Judaism," Cohen said.

In Islam, the ritual is slightly different; it's not in the Quran, and there are conflicting interpretations of Muslims' responsibility to get circumcised. But it's still an ingrained part of the faith; Muslims are the largest group that practices male circumcision in the world.

But outside of these minority faith communities, religion probably hasn't shaped American cultural views on circumcision. In the New Testament, circumcision isn't seen as necessary for salvation: "If you be circumcised, Christ shall profit you nothing," Paul says in Galatians.

Yet for Christians in America, this probably didn't shape their views on circumcision, said Cohen. "The original medical establishment that saw the benefits of circumcision was not a Jewish one—it was WASP-y," or white, Anglo-Saxon, and Protestant. As the procedure became more popular and common during the late 19th century and into the first part of the 20th, he said, "I don't think Christians worried about the fact that they're somehow defying what Paul said in the New Testament."

For most people, removing the foreskin was a strictly medical decision, even if it did have slight moral overtones. “A circumcised penis was seen as healthier, neater, cleaner—and that it would inhibit male masturbation. There was a terror of masturbation in American society," Cohen said.

According to Cohen, American circumcision hit its peak during the mid-20th century, partly coaxed along by the influence of the United States military. In his book On Circumcision, a doctor named Ed Schoen describes an anecdote from an American veteran who served in the navy during World War II. Upon their arrival at boot camp, new recruits were lined up and asked, "Are there any Jews in the group?"

My friend was shocked. He thought that Hitler might have won the war and, as a Jew, he was going to be sent to a concentration camp. ... Far from being interned, this group was told to go to the recreation area, enjoy themselves and report back to the barracks in an hour. The other inductees were told to drop their pants in preparation for an inspection of their genitals by a navy medic, a "short arm inspection." The medic went down the line checking the circumcision status of the young men ... and asking the uncircumcised men to retract the foreskin. Those with an unretractable or tight foreskin were sent to the infirmary to be circumcised.

"The U.S. army in World War II wanted men to be circumcised ... it was thought to reduce inflammation and masturbation," Cohen said. "That's the moment when circumcision became well-nigh universal among the white citizenry."