UNITED NATIONS (AP) — U.S. Secretary of State Rex Tillerson appealed to the international community, especially Russia and China, to stop the spread of nuclear weapons, calling North Korea a case study of the failure to prevent rogue states from obtaining weapons of mass destruction. U.S.-Russian relations are at a low point, but Tillerson recalled the cooperation between Washington and Moscow during the Soviet era, despite their Cold War rivalry, on measures to stop the threat of nuclear weapons proliferation.