Daylight Saving Time began in the First World War. The concept wasn’t new, and there had even been a bill introduced in the British Parliament in 1908, but the first implementation was Sommerzeit, which began on April 30th, 1916 by Imperial decree in Germany and Austria-Hungary. The purpose was to save coal because there was a shortage of coal miners. The idea caught on quickly, with the UK the first to follow on May 21st, 1916 and most other European countries in the subsequent months. The US established Daylight Saving Time on March 19th, 1918.
Here’s one of many good articles about the subject: