Guardians of the Flame is a portal fantasy series by author Joel Rosenberg, and arguably his best-known work.
The series progresses with the students choosing to live in the 'game world' and forming their own community, which is in part based on opposition to the ubiquitous slave trade.
The series then expands upon the students' "Home" in the fantasy realm and their effecting societal change.
[1] In the later books, the focus shifts from efforts to destroy the slave trade and on to various characters dealing with the changes in the fantasy world wrought by the former students (now mostly 40-somethings).
The final three books shift focus to a new set of protagonists, relegating the 'Other Siders' to supporting cast and cameo appearances.