The rejection of the Treaty of Versailles in 1919–1920 marked the dominance of isolationism in American foreign policy. Despite Roosevelt's Wilsonian background, he and Secretary of State Cordell Hull acted with great care not to provoke isolationist sentiment. The isolationist movement was bolstered in the early to mid-1930s by Senator Gerald Nye and others who succeeded in their effort to stop the "merchants of death" in the U.S. from selling arms abroad. This effort took the form of the Neutrality Acts; the president asked for, but was refused, a provision to give him the discretion to allow the sale of arms to victims of aggression. Focused on domestic policy, Roosevelt largely acquiesced to Congress's non-interventionist policies in the early-to-mid 1930s. In the interim, Fascist Italy under Benito Mussolini proceeded to overcome Ethiopia, and the Italians joined Nazi Germany under Adolf Hitler in supporting General Francisco Franco and the Nationalist cause in the Spanish Civil War. As that conflict drew to a close in early 1939, Roosevelt expressed regret in not aiding the Spanish Republicans. When Japan invaded China in 1937, isolationism limited Roosevelt's ability to aid China, despite atrocities like the Nanking Massacre and the USS Panay incident.