Backup cameras have been required on all new light vehicles in the United States built on or after May 1, 2018. Under Federal Motor Vehicle Safety Standard No. 111 (49 CFR 571.111), every new passenger car, SUV, pickup truck, van, bus and low-speed vehicle with a gross vehicle weight rating of 10,000 pounds (4,536 kg) or less must display a rearview image, after a phase-in that began on May 1, 2016. The image must show a zone roughly 10 feet wide and 20 feet deep directly behind the vehicle, and it must appear within 2.0 seconds of the driver shifting into reverse. The stated purpose of the rule is to reduce deaths and injuries that happen when a driver cannot see clearly behind the vehicle, such as children or older pedestrians being struck while a car backs up.
Source: 49 CFR 571.111, Federal Motor Vehicle Safety Standard No. 111: Rear visibility (eCFR)
Image: Backup camera view on a 2017 Honda Ridgeline dashboard display. Kelvin Eng via Wikimedia Commons, CC BY-SA 4.0.