Complex sentence: It was the first of Asimov's stories of the Black Widowers, an eccentric group of men who met once a month, which was based loosely upon the Trap Door Spiders, a stag-club of which Asimov was a member.
Split into simpler sentences: It was the first of Asimov's stories about the Black Widowers, an eccentric group of men who met once a month. The story is based loosely upon the Trap Door Spiders, a stag-club of which Asimov was a member.