It was the train…
Before mass transit was created there were many different time definitions, standards and criteria. Part of the reason was how long it took to get from one location to the next. The shift in the sun and moon were not discernible. In fact it was not important as the world was not connected and did business only locally.
But, things started changing in 1764 when English horologist John Harrison, discovered that a clock could be used to locate a ship’s position at sea with extraordinary accuracy.
Furthermore things really came to a head later when the American railroad was connected from one side of the nation to the next. In the beginning train conductors had over 300 different time zones for the rail stations. This quickly became a problem because none of them were connected. They shifted the 300 to 100 in the early 1800’s
It was November 18, 1883 that four standard time zones for the continental United States was introduced.
But how, what was the basis of measurement? Greenwhich….
“The Greenwich Observatory’s reputation for the reliability and accuracy in publications of its navigational data was one factor that contributed to the Greenwich Meridian’s popularity. Moreover, the shipping industry would benefit from having just one prime meridian. Many people informally recognized the Greenwich Meridian as the prime meridian prior to the International Meridian Conference in 1884.”
“The main factors that favored Greenwich as the site of the prime meridian were:
Britain had more shipping and ships using the Greenwich Meridian than the rest of the world put together (at the time). The British Nautical Almanac started these charts in 1767.
The Greenwich Observatory produced data of the highest quality for a long time.”
So it was America with it’s railroads and Britain with it’s ships that pushed the Prime meridian agenda.
“Standard time, in terms of time zones, was not established in United States law until the Act of March 19, 1918, sometimes called the Standard Time Act. The act also established daylight saving time in the nation. Daylight saving time was repealed in 1919, but standard time in time zones remained in law, with the Interstate Commerce Commission (ICC) having the authority over time zone boundaries.”
“Many countries adopted hourly time zones by the late 1920s. Many nations today use standard time zones but some places adopt half-hour deviations from standard time or use quarter hour deviations. Moreover, countries such as China use a single time zone even though their territory extends beyond the 15 degrees of longitude.”[SOURCE](http://www.timeanddate.com/time/time-zones-history.html)