From https://voat.co/u/dundundunnnnn

If you grew up Mormon in the first half of the 20th century, you were likely to be taught over and over–in Sunday School, genealogy, and priesthood lessons, in stake and general conferences, in church magazines, books, and pamphlets–that you were literally an Israelite, directly descended from Ephraim. This teaching would come in at least two forms:

1. The teaching one might call “Mormon Israelism” was that Ephraim’s descendants were scattered among all nations, but that almost all Mormons were Ephraimites (for some, even “pure” Ephraimites) because the people that had responded to the missionary message were the select few with Israel in their veins. It was taught (including by Joseph Smith) and assumed by some that the more pure the Israelite blood, the more open a person was to the Mormon message.

2. Somewhat in conflict with this, you would also have been taught Mormon Anglo or British Israelism: that almost all Mormons were Israelites (and to some, pure Israelites), because the Saints were of Northern European stock (largely British), which was the place the not-so-lost tribes (mainly Ephraim) had settled.

In the 20th century, the main church leaders and authors who preached Israelism and British Israelism were Church Historian and Apostle Joseph Fielding Smith, apostle and First Presidency member Anthony Ivins, Asst. Church Historian Andrew Jenson, and officers of the Utah Genealogical Society such as Archibald Bennett and James Anderson.

In dozens of articles, books, and general conference talks, these men played a significant role in teaching a couple of generations of Saints that they were literal descendants of Israel, with detailed proofs that the not-so-lost ten tribes had settled either Northern Europe or Great Britain taken directly from the prominent British-Israel works. Anderson, in God’s Covenant Race, From Patriarchal Times to the Present, a 1937 book published by the Deseret News Press, even claimed (incorrectly) Mormon credit for starting the British-Israel Movement through the church’s 1830s missionary work in England (154-155). The 1938 and later editions of the book included an appendix with 127 pages of articles copied verbatim from the “Anglo-Israel Federation” magazine Destiny.

One collection of Mormon British-Israelism teachings was the 1942 Sunday School course book, Birthright Blessings; its 48 lessons included topics such as “The Chosen Race Being Gathered,” “Early Israelite Colonies,” “Mound Builders of Europe,” “Sagas and Civilization of Scandinavia,” “Who Are the Anglo-Saxons?,” “Early Welsh Customs,” ” Ancient Irish Pedigrees,” and “The Royal House of David.”

A very similar collection was the 1937 Junior Genealogy Class manual, Children of the Covenant. Its 40 lessons covered most of the Birthright topics mentioned and others such as “A White and a Blessed People,” “The Day of Ephraim,” and “The New Race of Israel.” The activity for one of the lessons instructed students to “Write a one page explanation, and read it in class or in a public meeting, of the topic: “My Heritage as a Descendant of Ephraim.”

Articles preaching British Israelism and Mormon Israelism were also common in the quarterly journal of the Church’s Utah Genealogical and Historical Magazine.

Examples of this were the paired 1930 articles, “Mission of Ephraim,” by Joseph Fielding Smith, and “Children of Ephraim,” by Archibald Bennett.

The latter even contained a detailed explanation and ancestral charts explaining how the Norse God Odin (Woden) was ancestor of “most of the kingly and noble races of the north,” and therefore, of Anglo-Saxons and Mormons. Consequently, you can find Mormon family trees from that period that include both Odin and Thor (there’s a current example of this in my extended family). Odin is also discussed in detail in the Birthright Blessings and Children of the Covenant manuals, in a lesson called Sagas and Civilization of Scandinavia that recounts Icelander Snorri Sturluson’s Ynglinga Saga. Both books included a photo of a B.E.F. Fogelberg’s statute of Odin (the graphic at the top of this post).