On American assimilation; Puritan killjoys; Daenerys Targaryen:
Those hardcover books don’t put Halloween in American culture until sometime after the potato famine and mass immigration of many Irish/Scots in the 19th century, and state that this is mostly because Puritans -- those joy-killing revolutionaries -- hated Halloween (see: Salem Witch Trials, demonology, exorcisms, their reluctance to purchase face makeup, etc), and also the Scotch-Irish. And also people who might’ve slept with Hester Prynne.
The holiday wasn’t really celebrated outside of ethnic enclaves until the 20th century. In fact, the first documented act of “guising” in the Americas isn’t until 1911, and that was in Ontario, Canada, which is only technically America according to people who like maps. BUT Halloween was #trending! By 1919, a historian woman named Ruth Edna Kelley even wrote a book about its history, and mentioned “holding Scotch parties” and studying “old traditions”, and generally being kickass.