Prior to the late nineteenth century, timekeeping was a purely local phenomenon. Each town would set their clocks to noon when the sun reached its zenith each day. A clockmaker or town clock would be the "official" time and the citizens would set their pocket watches and clocks to the time of the town. Travel between cities meant having to change one's pocket watch upon arrival.
However, once railroads began to operate and move passengers and freight over the thousands of miles of rail line that covered North America, time became much more critical. In the early years of the railroads, the schedules were very confusing because each stop was based on a different local time.
Efficient rail transportation demanded a more uniform time-keeping system. Rather than turning to the federal governments of the United States and Canada to create a North American system of time zones, the powerful railroad companies took it upon themselves to create a new time code system. The companies agreed to divide the continent into four time zones; Eastern, Central, Mountain, and Pacific,1
Most Americans and Canadians quickly embraced their new time zones, since railroads were often their lifeblood and main link with the rest of the world. However, it was not until 1918 that Congress officially adopted the railroad time zones and put them under the supervision of the Interstate Commerce Commission. 2
Within a year of the change, 85%of cities in the U.S. were using standard time. Today, most major countries use a similar system of time zones aligned with meridians of longitude. 3
1Rosenberg, Matt, 2017. The History and Use of Time Zones. https://www.thoughtco.com/what-are-time-zones-1435358
2Onion, Amanda et al. 2019. Railroads create the first time zones. November 14. https://www.history.com/this-day-in-history/railroads-create-the-first-time-zones.
3 Sue, Caryl, 2013. Nov 18, 1883 CE: North American Time Zones Created. https://www.nationalgeographic.org/thisday/nov18/north-american-time-zones-created/