What is the meaning of the idiom "Like the Nation"?

Solution 1:

When I took a course on Mark Twain as an undergrad, the professor explained that "the nation" was a modification of "tarnation" which was itself a euphemism of "damnation" or "eternal damnation" (contracted) — euphemized because people in those days took damnation very seriously. So "the nation" would have been a euphemism of a euphemism, and presumably somewhat softer. "The very nation" would have been a logical intensifier for the contracted euphemism.

I don't have any references to cite, because the only corroborative mentions I can discover in a Google search are themselves unsourced opinions. But I trust my old Twain prof.

It is worth noting that Twain, in his autobiography, notes that he was an inveterate user of profanity until one day when his wife caught him in full fury, and calmly repeated back to him all the swear words he had just used. Hearing those words from her lips, he says, so shamed him that he sought henceforth to modify his speech accordingly.