There are no officially recognized beginning and ending dates for the Korean War, as neither the United States nor North Korea ever made an official declaration of war. The war also ended in a stalemate, meaning that North and South Korea are technically still at war, despite the fact that, as of 2014, the countries have few, if any, armed conflicts.
Although the exact dates vary, it is generally thought that the war began when U.S. forces arrived in Korea on July 1, 1950, one week after the DPRK invaded South Korea. Still, other sources put the beginning of the conflict back much further, pointing to conflicts between Russia and Japan over Korea that took place from the early 1900s up until the end of World War II.
Soon after U.S. forces arrived to help the South Koreans, Chinese forces also started to arrive in support of North Korea. The two groups then continued to fight against each other for almost three years, before the Americans and Chinese finally agreed to a cease-fire on July 27, 1953. This cease-fire agreement still continues in 2014, with North and South Korea being split along the demilitarized zone, which marks the border between communist North Korea and capitalist/democratic South Korea.