There is a similar thread just below this one that discusses feudalism. In that one I posted a link to a thread that directly addresses the question you ask. That thread is a good starting point for understanding a few of the issues.

Why is the term "feudalism" falling out of favor with historians: http://www.reddit.com/r/AskHistorians/comments/1ap2li/why_is_the_term_feudalism_falling_out_of_favor/