IIRC, several types of Karate claimed the title American Karate early on. This was due to several reasons. EPAK because EP was an American and the system was composed here. TKD occurred due to the political splits that were happening in the 60's and early 70's. From what I can tell, several of the American-based school and systems broke off from their Korean roots and added/deleted items from their corriculum. With this said, and a little contrary to the above statement, in the DFW area American Karate (TKD) sticks closer to the original fighting art and is not near as sporterized as the McDojos. I originally took TKD from a group under Jim Benko call Midwest TKD Association. This is now called the World TKD Association, I believe. The teachings then were totally focused on fighting and not sport. There were about 30+ self-defence techniques to black.
I ran into an American Karate instructor from the DFW area and found that the system that they were teaching was almost identical to the TKD that I was taught decades earlier. Hyungs were the same. Focus was the same. Etc. I believe he was under Pat Burleson. If I was to do TKD again, I would seek out one of these schools. However, I don't think my old airframe could keep up with it.
Also, during the 50s-70s it was also a marketing issue. In the 40s-mid sixties, anything Japanese was considered bad (WWII and quality of products. Of course, in the early 70s, this view changed dramatically.) During that time, things called American Karate gained fame and other styles tried to ride this wave.
OG