The clocks change due to Daylight Saving Time, which starts on the second Sunday in March and ends on the first Sunday in November, as of 2014. People in participating states and territories change their clocks at 2 a.m. on these days.
In 1918, the United States used Daylight Saving Time to conserve resources needed to fight in World War I. The law was repealed, but the country was put back on Daylight Saving Time in 1942 because of World War II. After World War II ended, some counties kept following Daylight Saving Time. This created confusion for the transportation and broadcasting industries. As a result, Congress passed the Uniform Time Act of 1966 to set official start and end dates for Daylight Saving Time. States and territories were not required to participate, but if they did, they had to adhere to the dates and times outlined in the act.