Daylight savings time was initiated as an energy saving measure. By moving the clocks ahead one hour, people could take advantage of an extra hour of daylight. Benjamin Franklin came up with the idea in 1784, but it wasn't implemented in the United States until World War I.
President Woodrow Wilson signed the law initiating U.S. Daylight Saving Time in 1918. After seven months, the law was repealed, with only a few cities electing to continue DST on their own. After the bombing of Pearl Harbor and the United States' entering into World War II, DST was again implemented, only this time it was called "War Time."
After the war ended, cities and states were free to observe DST, or not. This caused mass confusion in the broadcasting and transportation industries. In 1966, the Uniform Time Act was passed, which mandated DST from April to October each year. States could still refuse by passing a local law.
As of 2015, DST is observed from mid-March through the beginning of November in all states except for Hawaii and parts of Arizona. The schedule is based on the Energy Policy Act of 2005, which made DST strictly an energy saver, rather than a wartime measure.