You may be interested in the “Time zones and time differences” section of the Popular Questions pages, found in the sidebar.

Well.....during the american industrial revolution train track building was big business, and the train drivers who delivered stuff always worried about being late. Before hand, people already had time zones but it was very unorganized and no system and there were many more time zones than there are now. The people who drove the trains proposed that the United States be separated into 4 different time zones to fix this problem.