At least when it comes to demographics:
Maybe the most surprising thing here is that most of the US’s religious diversity comes not from religious minorities, who in total are only 5.3 percent of the population, but from the 16 percent of Americans who are unaffiliated. Part of that has to do with the fact that, for all of the US’s racial diversity, many of those racial minority groups tend to Christian: most African-Americans, certainly most Latinos, and a significant share of Asian-Americans.
Now compare the US to France and you’ll see two things: that France has almost twice as many unaffiliateds, as a share of … overall population, and eight times as many Muslims. This comparison also gets to a shortcoming in Pew’s metric, though. Something this data does not show is intra-Christian diversity: the US has lots of different Christian groups, whereas French Christians are overwhelmingly Catholic. Diversity between Catholics and Protestants alone has been hugely important for US religious history. While Americans may not be super-diverse along broader religious categories, that intra-Christian diversity has been a real challenge in the US, and one that the country has done an unusually good job of dealing with.
Emma Green connects these findings to another Pew study on religious violence, noting that “some of the least religiously diverse countries also experience some of the most religious violence”: