Complex sentence: His literary career also benefited greatly from his relationships with Mary Austin and H.L. Mencken, who provided an outlet for his early journalism and floated the idea for his first book, a 1929 biography of popular writer and sometime Californian Ambrose Bierce.
Split into simpler sentences: His literary career also benefited greatly from his relationships with Mary Austin and H.L. Mencken. Mencken provided an outlet for McWilliams's early journalism and floated the idea for his first book, a 1929 biography of popular writer and sometime Californian Ambrose Bierce.