Armistice negotiations began at the behest of the Soviets in June 195 1 and dragged on for two years. It took until July 26 even to establish an agenda for the conference. The participants decided that an armistice would require agreement on a demarcation line and demilitarized zone, impartial supervision of the truce, and arrangements for return of prisoners of war. The toughest single issue involved the disposition of POWs. U.N. negotiators wanted prisoners to decide for themselves whether they would return home; the communists, fearful of mass defection, held out for mandatory repatriation. In an effort to break the negotiation stalemate, General Mark Clark, who had succeeded Ridgway, stepped up bombing raids on North Korea. At last, during April 1953, the POW issue was resolved; a compromise permitted freed prisoners to choose sides, but under supervision of a neutral commission.