Complex sentence: Along with co-publisher Gary Groth, Thompson has for almost thirty years used his position to further the cause of alternative comics in the American market, as well as to bring the work of high-quality European cartoonists to American readers.
Split into simpler sentences: Along with co-publisher Gary Groth, Thompson has for almost thirty years used his position to further the cause of alternative comics in the American market. In addition, Thompson has made it his business to bring the work of European cartoonists to American readers.