The Neutrality Acts were laws passed by the United States Congress in the 1930s, stopping the sale of arms or loans of money to nations at war. They were spurred by the growth in isolationism in the US following its costly involvement in World War I, and sought to ensure that the US would not become entangled again in foreign conflicts. The acts were largely repealed in 1941, in the face of German submarine attacks on U.S. vessels and the Japanese attack on Pearl Harbor.