I am trying to understand the association, evolution, and adaptation
of American Buddhism compared with traditional (original, if
appropriate) Buddhism.

How do the two differ?  
What are the main reasons American Buddhism is different/similar?
Does American Buddhism stay "true" to the original Buddhist ideals?

Basically, I am trying to understand how "Modern" American Buddhism is
different and how why and when it has adapted to what it is today.

My interest in Buddhist history has reached a slight wall, and I would
appreciate an answer with references and quotes where I can read up
and continue my passion.

Thank you!

Detail asnwer is available here.

http://en.wikipedia.org/wiki/Buddhism_in_America

Let me know if you have any more questions.

Wow thank you, that helped very much actually.  I haven't finished
reading it all, but it's a great start - thanks!

You are welcome. I was fun looking up somthing that I am interested in.

At the first conference on Buddhism in America, Boston, January 1997,
I heard one of the keynote speakers say that Buddhism had moved from
Eastern teachers teaching Eastern students to Eastern teachers
teaching Western students and that we have now reached the stage of
fully qualified Western teachers teaching Western students.  Much of
the conference centered on the meaning of that transition and how it
is transforming Buddhism--how Western Buddhism is becoming a
recognized branch of Buddhism in its own right.  The proceedings of
that conference may still be available in book form.  I know that at
least four more conferences were held; I attended three of them.

I like what Steve Smith wrote about this subject in the foreword to
one of Charlotte Joko Beck's books, "Nothing Special:  Living Zen." 
Forgive my faulty memory, but this is how I remember it:  he wrote
words to this effect--"If Zen is to make the transition to the West,
it must acquire a Western idiom.  'Chop wood, carry water' must become
"Make love, drive freeway.'"  That transformation is very far from
being accomplished, partly, I think, because there is a great deal of
beauty and meaning in the traditional forms and language as well as
the link to the lineage of dharma transmission.  But Buddhism itself
can't be something essentially different from continent to continent. 
If it couldn't survive crossing a minor cultural boundary between
contemporaneous human beings, it certainly wouldn't be a resilient
enough philosophy to stand up to a person's actual life challenges.

My personal opinion--
Archae0pteryx
(not a researcher)

Correction:  I know that at least four conferences were held; I
attended three of them.  (Not "four more," which would mean a total of
five.  That might be the case, but I do not have knowledge of it.)