Short answers, pulled from the story.
The phrase story arc first appeared in print during 1973 inside a Time Magazine review of the film The Friends of Eddie Coyle. A critic wrote that the director handled action sequences without sacrificing pacing or suspenseful development of the story's arc.
NBC aired The Fifth Horseman in 1946 as a four-episode docudrama serial about a hypothetical nuclear holocaust. That program spanned nearly two full future decades within its short run and demonstrated how serialized storytelling could stretch across time.
Neon Genesis Evangelion stands as one example of a single story arc covering exactly twenty-six episodes with no breaks between major plot points. Most anime series shorter than twenty-six chapters function as a single arc spanning all available installments which makes syndication difficult when watched in isolation.
Joseph Campbell laid out his theory of the monomyth in The Hero with a Thousand Faces to explain how heroes journey through specific stages of growth. Christopher Vogler applied that same theory directly to western storytelling in his book The Writer's Journey: Mythic Structure for Writers.
American comic book publishers began writing series in four- or six-issue arcs during recent years to make stories easier to package as trade paperbacks for resale. Shorter story arcs allow casual readers to enter the narrative without needing to understand never-ending continuity that once characterized US comics.