J. Hoberman at The Nation:
Magazine-like compilations of newspaper comic strips first appeared in the early 1930s, around the time that newspaper strips increasingly became vehicles for action and adventure tales. The mid-’30s saw the emergence of original comic books with titles like Thrilling Wonder Stories. These began to flourish, and the year 1938 brought their apotheosis with the creation of Superman. Soon, each monthly installment of his adventures, published in National Periodical’s Action Comics, was selling nearly 1 million copies.
Located in New York City, the comic book industry was a sort of sweatshop Hollywood. Overhead was low, piecework was the norm, and business was good, albeit exploitative.
more here.