After one season of good reviews, but mediocre ratings, ABC offered to renew the series if Producer Irwin Allen would cut his budget by one-third. He refused, and the series was cancelled, to be replaced in the fall of 1967 by Custer (1967).
Many episodes made extensive use of stock footage from the 20th Century Fox film library, which allowed Irwin Allen to do shows against an "epic" backdrop that could not have been done on a television budget.