If you just pick a state and start searching and read all the fine print, you will usually find something like this....
Ohio
Lawriter - ORC - 4513.20 Brake equipment for vehicles.
(4) When operated upon the highways of this state, the following vehicles shall be equipped with brakes adequate to control the movement of and to stop and to hold the vehicle, designed to be applied by the driver of the towing motor vehicle from its cab, and also designed and connected so that,
in case of a breakaway of the towed vehicle, the brakes shall be automatically applied:
(a) Except as otherwise provided in this section, every trailer or semitrailer, except a pole trailer, with an empty weight of two thousand pounds or more, manufactured or assembled on or after January 1, 1942;
(b) Every manufactured home or travel trailer with an empty weight of two thousand pounds or more, manufactured or assembled on or after January 1, 2001.