Complex sentence: The major theme of "All My Sons" is Arthur Miller's belief that people have a wider responsibility to the society in which they live, and this is something that Chris, Joe's son, is aware of and believes in.
Split into simpler sentences: The major theme of "All My Sons" is the belief that people have a wider responsibility to the society in which they live. This is something that Chris, Joe's son, is aware of and believes in.