Conversation so far:
What was Edward Sapir moving on with?
Edward Sapir was now more preoccupied with testing hypotheses about historical relationships between the Na-Dene languages than with documenting endangered languages, in effect becoming a theoretician.
Are there interesting aspects to Edward Sapir becoming a linguistic theoretician?
During his period in Canada, Edward Sapir came into his own as the leading figure in linguistics in North America.
How did Edward Sapir come into his own as the leading figure in linguistics in North America?
Edward Sapir laid out an approach to using linguistics to study the prehistory of Native American cultures. Particularly important for establishing him in the field was his seminal book Language.

Question: What are some other accomplishments?
Self-contained rewrite: What are some other of Edward Sapir's accomplishments besides becoming the leading figure in linguistics in North America?