In December 1950, Truman declared a national emergency in response to the Korean War.[93] The First Indochina War continued in Vietnam, in which communist forces in the north fought against French Union forces in the south.[93] The US expanded the Radio Free Europe broadcasting system in an effort to promote Western political ideals in Eastern Europe.[93] In March 1951, American communists Julius and Ethel Rosenberg were convicted of spying for the Soviet Union.[93] In 1952, the US exploded its first hydrogen bomb, and the Soviet Union followed suit in 1953.[93]