Early cars had a foot pedal as well as a hand brake. Typically the foot pedal braked the driveshaft and the hand braked the wheel brakes.
So the backup was already in place even in the earliest of cars.
Calling it a parking brake was advised by the legal departments of car makers since it was far less powerful than the full system. Still the same cable operated system
Now those emergency or parking brakes are electrically operated on some cars. No cables, just a small electric motor that applies the rear brakes.