The American fried chicken sandwich is a genre, and the thing that makes it a genre rather than a recipe is that the fillet brings every texture and the rest of the build exists only to keep that texture intact. A boneless piece of chicken is brined, breaded, and fried, then closed inside a soft bun with pickle and a sauce. Strip away the regional arguments and that is the fixed grammar everywhere it is made: the crust is the sandwich, and the bun, the pickle, and the sauce are the cool, acidic, yielding frame whose only job is to keep a hot hard salty fillet from reading as one heavy note. The defining fact is that nothing in the build is allowed to compete with the coating.
The craft is a contradiction managed well. The fillet has to be thick enough to stay juicy but even enough to cook through before the crust burns, which is why it is brined or buttermilk-soaked ahead of the dredge and often pounded to an even plane. The crust has to be craggy, because a smooth coating cannot hold seasoning or stay crisp, so the breading is pressed loose and dredged so it blisters in the oil. Then the closed-sandwich problem: a crisp crust trapped against a soft bun steams itself soft, so the sauce goes on the bun rather than over the coating and the bun is chosen pillowy and faintly sweet so it compresses to the fillet instead of fighting it. Flat dill pickle is the single sharpest counter to fried fat and is doing structural work, not decoration. It is a fast-food and lunch-counter build at its core, fried to order and assembled in seconds, eaten before the crust gives way to its own steam.
The variations are a national argument conducted mostly through chains and regional styles, and they belong in their own articles rather than crowded in here. The Nashville hot version lacquers the crust in a fat-borne cayenne paste built to be a dare. The Buffalo build borrows the wing's hot sauce and blue cheese. The Korean-American style double-fries for a thinner, glassier shell under a soy-garlic or gochujang glaze. The biscuit version trades the bun for a flaky buttermilk biscuit and changes which half of the sandwich leads. The grilled version drops the crust entirely and becomes something else. Each keeps the founding rule and changes one thing, which is exactly the impulse that gave this sandwich a name of its own.