Top 12 American Prog Albums

Not sure I can squeeze out 12....

Dream Theater - Images And Words

King's X - Gretchen Goes To Nebraska

Kansas - Leftoverture

Faith No More - The Real Thing

Blue Oyster Cult - Imaginos (thought they were British until reading this thread!)

Metallica - ...And Justice For All

Neil Morse Band - The Similitude Of A Dream

Devin Townsend - Empath - if that's allowed?  Is this USA only or North American?

Struggling now, so would have to fill out with more DT, DT and KX (but everyone else seems to be restricting it to one per artist....)

Well, narrowing a multi-national group down to a single nationality is always going to involve some arbitrary simplification. For the record, I consider Weather Report and Talking Heads American bands despite the Austrian and British origins of their respective leaders, but Mahavishnu Orchestra is a special case because I see it as much more of a manifestation of the individual wishes of the band leader (this is reflected by how McLaughlin wrote virtually every song ever recorded by the band, and the fact that "Mahavishnu" was the name that McLaughlin adopted for himself after becoming a follower of Sri Chinmoy, so you could say he named the band after himself). Considering how the actual music fits in with the American jazz fusion tradition of the time, I do agree with you though that it's far more useful for historical purposes to categorize the Orchestra as an American band.

In my opinion, it doesn't give much meaning, not to consider Mahavishnu Orchestra as an American band, and a part of the country's Jazz>Rock scene - the same considering Weather Report with the Austrian Joe Zawinul as one of the two leaders, and Miles Davis being a very important name in relation to both bands.