In 1933 Dorothy Detzer, executive secretary of the Women's International League for Peace and Freedom, approached Gerald Nye, George Norris and Robert La Follette and asked them to instigate a Senate investigation into the international munitions industry. On 8th February, 1934, Nye submitted a Senate Resolution calling for an investigation of the munitions industry by the Senate Foreign Relations Committee under Key Pittman of Nevada. Pittman disliked the idea and the resolution was referred to the Military Affairs Committee. It was eventually combined with one introduced earlier by Arthur H. Vandenberg of Michigan, who sought to take the profits out of war.

The Military Affairs Committee accepted the proposal and as well as Nye and Vandenberg, the Munitions Investigating Committee included James P. Pope of Idaho, Homer T. Bone of Washington, Joel B. Clark of Missouri, Walter F. George of Georgia and W. Warren Barbour of New Jersey. John T. Flynn, a writer with the New Republic magazine, was appointed as an advisor and Alger Hiss as the committee's legal assistant.

Public hearings before the Munitions Investigating Committee began on 4th September, 1934. In the reports published by the committee it was claimed that there was a strong link between the American government's decision to enter the First World War and the lobbying of the munitions industry. The committee was also highly critical of the nation's bankers. In a speech Nye argued that "the record of facts makes it altogether fair to say that these bankers were in the heart and center of a system that made our going to war inevitable".

Several members of Congress, including Gerald Nye, Arthur H. Vandenberg, William Borah and Robert La Follette, pushed very hard for the passing of the 1935 Neutrality Act. President Franklin D. Roosevelt objected to this measure and lobbied for embargo provisions that would allow him to impose sanctions selectively. This was rejected by Congress and the act, signed on 31st August, imposed a general embargo on trading in arms and war materials with all parties in a war.

The 1936 Neutrality Act, passed in February of that year, renewed the provisions of the 1935 act for another 14 months. It also forbade all loans or credits to belligerents. However, this act did not cover "civil wars" or materials such as trucks and oil. During the Spanish Civil War some U.S. companies such as Texaco, Standard Oil, Ford Motor Company and General Motors sold such items to General Francisco Franco on credit.