New surveys show Americans' membership in communities of worship has declined sharply in recent years, with less than 50% of the country belonging to a church, synagogue or mosque.

Why it matters: The accelerating trend towards a more secular America represents a fundamental change in the national character, one that will have major ramifications for politics and even social cohesion.

By the numbers: A Gallup poll released last week found just 47% of Americans reported belonging to a house of worship, down from 50% in 2018 and 70% as recently as 1999.

• The shift away from organized religion is a 21st century phenomenon. U.S. religious membership was 73% when Gallup first measured it in 1937, and stayed above 70% for the next six decades.

Context: The decline in membership is primarily driven by a sharp rise in the "nones" — Americans who express no religious preference.

• The percentage of Americans who do not identify with any religion rose from 8% between 1998 and 2000 to 21% over the past three years, while the percentage of nones who do not belong to a house of worship has risen as well.

The big picture: The story of a more secular America is chiefly — though not entirely — one of generational change.

• Membership in houses of worship is correlates with age, with the oldest Americans much more likely to be church members than younger adults.
• But while church membership is lower among younger generations, the dropoff is particularly stark among millennials and Gen Z, who are about 30 percentage points lower than Americans born before 1946, compared to 8 points and 16 points respectively for baby boomers and Gen X.
• Children who grow up without organized religion are less likely to join houses of worship when they become adults, so it stands to reason that the secularization trend will only continue in the future, barring major demographic or cultural changes.

Yes, but: Generational replacement — the idea that society-wide changes in values between the young and the old can be attributed to their different circumstances growing up — doesn't tell the entire story.

• Even the oldest Americans have seen a slight rise in the percentage of nones, while 20% of Gen Xers report no religious affiliation, up from 11% in 1999.

Details: Whatever their religious practices, Americans are increasingly rejecting many of the moral precepts found in most major religions.

• A 2017 Gallup poll found a significant majority of Americans believe practices like birth control, divorce, extramarital sex, gay and lesbian relations are all morally acceptable.
• In a piece last year for Foreign Affairs, the political scientist Ronald F. Inglehart argued that as birthrates have dropped thanks in part to contraception and falling infant mortality, modern societies have become less observant "because they no longer need to uphold the kinds of gender and sexual norms that the major world religions have instilled for centuries."

The catch: Just because conventional religious practice is on the decline doesn't mean Americans will have no need to fill what the journalist Murtaza Hussain calls the country's "God-shaped hole."

• While the earlier phases of the civil rights movement were built on the strength of the Black church, today many young people are flocking to campaigns like Black Lives Matter that aren't religious in nature, but often adopt the language of religion, spirituality and justice.
• "Political debates over what America is supposed to mean have taken on the character of theological disputations," Shadi Hamid, a senior fellow at the Brookings Institution, wrote in a recent Atlantic essay. "This is what religion without religion looks like."

What's next: As religion decreasingly becomes something Americans practice, it may instead become another identity, subsumed into the ongoing culture wars.

• The trend may also shake up the electorate. The journalist Matt Yglesias noted that when a white person switches from being Christian to non-affiliated, they are more likely to become a Democrat, "but when a Black person makes the same switch, the correlation goes in the other direction."
• That could help explain the fairly secular Donald Trump having partial success in increasing the GOP's share of the non-white vote in 2020.

The bottom line: The U.S. remains an unusually religious country, with more than seven in 10 Americans still affiliating with some organized religion, according to the Gallup poll.

• But conventional religion's power is on the wane, and it might take a miracle for that to change.