On 9 April, German forces invaded Denmark and Norway. On the same day Hitler proclaimed the birth of the Greater Germanic Reich, his vision of a united empire of Germanic nations of Europe in which the Dutch, Flemish, and Scandinavians were joined into a "racially pure" polity under German leadership. In May 1940, Germany attacked France, and conquered Luxembourg, the Netherlands, and Belgium. These victories prompted Mussolini to have Italy join forces with Hitler on 10 June. France and Germany signed an armistice on 22 June. Kershaw notes that Hitler's popularity within Germany – and German support for the war – reached its peak when he returned to Berlin on 6 July from his tour of Paris. Following the unexpected swift victory, Hitler promoted twelve generals to the rank of field marshal during the 1940 Field Marshal Ceremony.