A quick history of the sonnet form, by Robert Pinsky. Extra credit for mentioning Shakespeare, but then never actually using a Shakespeare sonnet as one of his many examples of the evolution of the form.
Shakespeare wrote his sonnets as part of a literary vogue, the great sonnet fad of the 1590s. Inspired by Sir Philip Sidney's sequence "Astrophil and Stella" (itself based on the Italian sonnets of Petrarch and popularized via early, Napster-like piracy), English poets and booksellers of that decade produced hundreds of sonnet sequences. The product in each case was a series of witty, hyperbolic 14-line love poems, addressed to a lady who, in theory, would be flattered and won by the poet's elaborate, inventive descriptions of her tremendous beauty, her cruel resistance, and the agony she inflicted on the author. She tortures him with her beauty and coldness, he says; and yet his praises, and his clever descriptions of the pain she causes him, will make her immortal.
When you put it like that, it makes the whole Fair Youth / Dark Lady autobiographical conspiracy theories sound sort of…dumb?