Final answer:
The overall claim of Mark Twain's essay is expressed in the sentence focusing on the uniqueness of the humorous story as American and its reliance on the manner of telling, distinguishing it from English comic stories and French witty stories which depend on the actual content.
Step-by-step explanation:
The sentence from Mark Twain's "How to Tell a Story" that most clearly states the overall claim is: "The humorous story is American, the comic story is English, the witty story is French. The humorous story depends for its effect upon the manner of the telling; the comic story and the witty story upon the matter." This sentence encapsulates Twain's main argument that different types of stories depend on different elements to achieve their effects, with the humorous story being distinctly American and relying on the storyteller's delivery rather than the content itself. Mark Twain is renowned for his writing and his insights into storytelling are informed by his experiences and his analysis of what makes a story humorous.