Hi. Long time reader, first time poster. For which reason I'm going to keep this short, and limit myself to just twenty words out of a single paragraph. But that small number of words may include the highest concentration of badhistory that I have ever encountered. It comes from Harrison Salisbury's 900 Days: The Siege of Leningrad (1969). Here's the paragraph, the timeline being 1940-1941:

Among the nationalist groups in Lithuania were the Union of Lithuanians, the Front of Lithuanian Activists and the Committee for Rescuing Lithuania. In Latvia they included the Perkinkrusts, and in Estonia the underground Legion of the East and the Committee of Rescue, otherwise known as the Izmailites and the Kaitzelites. Erna battalions to carry out diversions behind the lines of the Red Army.

Let's walk through the bit about Estonia, because that's the one I know about. I suspect the Latvian and Lithuanian parts are just as wrong. Google tells me that Pērkonkrusts is misspelled, unsurprisingly, because:

Kaitzelites. This is a gibberish nonsense version of "kaitseliit", which translates to "defence union" and is and was a generic name for the Estonian military. It's not some special group, it's just a general expression. It's as underground and special as "the army".

Izmailites. I have to disappoint you all. The Old Man of the Mountain was not in fact a freedom fighter for Estonia. This is another made up word. It took me a while to get what this was supposed to be. It's a gibberish nonsense version of "isamaaliit" (translates to "Fatherland Union"), a random political organization that functioned from 1935 to 1940. It was then disbanded, and I have no info of this random group being in any way underground or resistant-cy.

But this is the linguistic gibberish part. Surely the author simply didn't understand the language, and therefore this should have been posted at r/badlinguistics instead. But no!

Legion of the East. No such thing has ever existed. There was an Estonian Legion during WWI, and there was also the Estonian SS Legion during WWII. Which was established in 1942, but more importantly, an SS legion is not what you would call "underground".

Committee for Rescue. In an amazing twist, we for the first time have a thing that actually existed. Well, kind of. I suppose it's an understandable translation of what is more commonly known as the Salvation Committee. This was a group of three people who laid the foundation for the newly minted Republic of Estonia. It existed as a political entity for all of five days, after which it transferred power to the first provisional government of Estonia. In 1918.

So that's four badhistories in 20 words. Must be some sort of a record.

Sources: I don't know how to provide proper sources for made up words and things that don't exist.