What is the difference between African and Japanese drumming styles? 
When I listen to them, they sound similar - what are the specific
differences? Longer beats, shorter beats, faster patterns, etc.

http://www.earthdrum.com/rhythms_of_the_earth.htm

perhaps Morwen Two Feathers can answer this question for you?

There are many books available that explain the differences of
drumming within specific cultures.  I would suggest giving
www.steveweissmusic.com a call.  Ask to speak with the librarian, and
he should be able to get you the book you need.  They are really the
only good source of percussion literature that I know of.