Conversation so far:
When did Steven Seagal start martial arts?
Seagal moved to Japan at some point between 1971 and 1973.
Why did he move to Japan?
CANNOTANSWER.
DId he make any movies while in Japan?
CANNOTANSWER.
What did he do that had to do with martial arts?
Seagal initially returned to Taos, New Mexico, with his student (and later film stuntman) Craig Dunn, where they opened a dojo.

Question: How long did they have the dojo?
Self-contained rewrite: How long did Steven Seagal and Craig Dunn have their dojo