[TangoTrotFox]

Judaism is very different than most religions in that it doesn't try to spread, but is instead quite insular. If you want to convert it's a big deal with study, testing, and culminating with a literal certificate of conversion - that can be revoked. It's also very unique in that Jewish Orthodoxy considers it 'genetic'. If your mother was a Jew, you are a Jew - regardless of whether you consider yourself e.g. an atheist.

The majority of Jews today (in the ballpark of 75%) are Ashkenazi Jews which is a sort of 'race' in that they share a very recent common ancestor -- which is also why so many Jews share common physical features. All of this is very different than other religions, even other Abrahamic religions. So it is not inconsistent that state that Jews are an ethnic group, but other religious groups are not.

[kolpa]

Orthodoxy is only one small part of Judaism and Jews.

> If you want to convert it's a big deal with study, testing, and culminating with a literal certificate of conversion - that can be revoked.

https://judaism.stackexchange.com/questions/50602/can-conver...

Only in narrow areas, such as modern State of Israel (which is a blip in Jewish history, and not the world government of Jews), which very special circumstances.

It's complicated.

Also, you can be a non-Jewish woman, marry a Jewish man, and have Jewish children, who an Orthodox Jew might call non-Jewish children, but those children and their descendants and neighbors may never think are "not Jewish"

[TangoTrotFox]

You have things reversed. What you see today is an extremely rapid reformation upon reformation of Judaism. This is the blip in Jewish history. However, what has led up to today is the product of what we would consider orthodox Judaism, which of course was simply called Judaism.

For instance, in the past interfaith marriage was not only frowned upon but something that would likely result in individuals facing exile from the Jewish community. This, for instance, is why most Jews today share so many distinct physical and other characteristics. In searching for some interesting numbers I came upon this article [1] which you might find interesting - it discusses the ongoing "reformation" of Judaism. The reason I put reformation in quotes is because I think it's "reforming" in the way that most religions are today - it's fading. And I think a century it will probably make no more sense to refer to Jews as an ethnic group than it would to refer to Irish Americans as an ethic group today. However, as of today Jews most certainly remain an ethic group by most all facets of the word.

[1] - https://www.nytimes.com/2013/10/01/us/poll-shows-major-shift...