http://www.history.com/

While calls for daylight saving date back hundreds of years, the first practical
attempt to “spring forward, and fall back” began as a conservation measure
during World War I. In April 1916, Germany implemented the world’s first
clock shift as part of a plan to save on electricity and divert extra coal to their
soldiers on the front. Many other nations soon followed suit, including the
United States in 1918.

Daylight saving was widely regarded as a wartime measure, however, and
many countries reverted to standard time after the fighting ended. It would
take more than 20 years and another World War before the practice became
permanent.