As the decade of the 1950s opened, war erupted on the Korean peninsula, which had been split in the aftermath of the Second World War at the 38th Parallel. On 25 June 1950, the army of the communist North Korea crossed the border into South Korea. United States President Harry Truman interrupted a long weekend at his home in Independence, Missouri, to return to the capitol, where, five days later, he authorized General Douglas MacArthur to lead American ground forces to repel the invasion. Also in 1950, Senator Joseph McCarthy of Wisconsin accused State Department employees and many members of the American literary, film, and theatrical communities of being members of the Communist Party. The U.S. Atomic Energy Commission constructed the first nuclear reactor for power production, and in late November, the Chinese entered the Korean War and mounted a counteroffensive into South Korea.