provides that "no state has the right to intervene in the internal or external affairs of another". Roosevelt, World War II, and its aftermath: 1933–1947 Spanish Civil War: 1936–1939 In the 1930s, the United States entered the period of deep isolationism, rejecting international conferences, and focusing mostly on reciprocal tariff agreements with smaller countries of Latin America. When the Spanish Civil War erupted in 1936, the United States remained neutral and banned arms sales to either side. This was in line with both American neutrality policies, and with a Europe-wide agreement to not sell arms for use in the Spanish war lest it escalate into a world war. Congress endorsed the embargo by a near-unanimous vote. Only armaments were embargoed; American companies could sell oil and supplies to both sides of the fight. Roosevelt quietly favored the left-wing Republican (or "Loyalist") government, but intense pressure by American Catholics forced him to maintain a policy of neutrality. The Catholics were outraged by the systematic torture, rape and execution of priests, bishops, and nuns by anarchist elements of the Loyalist coalition. This successful pressure on Roosevelt was one of the handful of foreign policy successes notched by Catholic pressures on the White House in the 20th century. Germany and Italy provided munitions, and air support, and troops to the Nationalists, led by Francisco Franco. The Soviet Union provided aid to the Loyalist government, and mobilized thousands of volunteers to fight, including several hundred from the United States in the Abraham Lincoln Battalion. All along the Spanish military forces supported the nationalists, and they steadily pushed the government forces back. By 1938, however, Roosevelt was planning to secretly send American warplanes through France to the desperate Loyalists. His senior diplomats warned that this would worsen the European crisis, so Roosevelt desisted. Adolf Hitler and Franco mutually disliked one another, and Franco repeatedly manipulated Hitler for his own benefit during World War II. Franco sheltered Jewish refugees escaping through France and never turned over the Spanish Jews to Nazi Germany as requested, and when during the Second World War the Blue Division was dispatched to help the Germans, it was forbidden to fight against the Western Allies, and was limited only to fighting the Soviets. Coming of War: 1937–1941 President Roosevelt tried to avoid repeating what he saw as Woodrow Wilson's mistakes in World War I. He often made exactly the opposite decision. Wilson