Mark Twain’s career began during the Civil War. At that time he was working as a newspaper man.

Mark Twain’s Civil War began during his writing career when he was working as a newspaper man.

Mark Twain’s writing career began during the Civil War when he was working as a newspaper man.

Mark Twain’s writing career began during the newspaper man when the Civil War was working.

Mark Twain began as a newspaper man during the Civil War when his writing career worked.