Final answer:
The U.S. maintained neutrality during the Spanish Civil War due to isolationist policies and the Neutrality Acts, despite the violation of non-intervention agreements by Germany and Italy who supported Franco's forces with troops and the Luftwaffe.
Step-by-step explanation:
U.S. Neutrality in the Spanish Civil War
In the 1930s, the United States sought to avoid entanglement in foreign conflicts. With the specter of the First World War still looming, U.S. foreign policy was heavily influenced by the desire for isolationism. This was reflected in the U.S.'s approach to the Spanish Civil War. Although the war was a precursor to World War II, highlighting the rise of fascism in Europe, the U.S. maintained a strict policy of neutrality due to fear of entering another war and the influence of the Neutrality Acts passed by Congress. These acts prohibited the export of arms and the making of loans to belligerent nations.
German and Italian support for Franco's Nationalist forces violated the non-intervention agreement. Still, these countries, unlike the U.S., actively sent aid, including troops and the feared Luftwaffe, to Spain. This not only tipped the balance of the war in favor of the Nationalists but also provided Germany and Italy with an opportunity to test their military might prior to World War II.
Despite the lack of official support, American volunteers, known as the Abraham Lincoln Brigade, joined the fight on the side of the Spanish Republicans. Nevertheless, U.S. neutrality effectively curtailed any significant aid from the government, leaving the Republicans at a severe disadvantage. This policy continued until the fall of the Spanish Republic in 1939, prefacing the outbreak of World War II.