Britain, France, the United States, Canada and eight other western European countries signed the North Atlantic Treaty of April 1949, establishing the North Atlantic Treaty Organization (NATO). That August, the first Soviet atomic device was detonated in Semipalatinsk, Kazakh SSR. Following Soviet refusals to participate in a German rebuilding effort set forth by western European countries in 1948, the US, Britain and France spearheaded the establishment of West Germany from the three Western zones of occupation in April 1949. The Soviet Union proclaimed its zone of occupation in Germany the German Democratic Republic that October.