The Spanish Civil War, which began in July 1936, was the most significant of the conflicts that foreshadowed World War II.
The war forced the world to take sides. Russia contributed military assistance to the cause of the newly elected Republican government, while Germany and Italy backed the Fascist rebels, followers of Generalissimo Franco, who were known as Nationalists.
Many countries, including the United States, chose to stay neutral, believing that involvement would lead to a further war in Europe. In spite of this, many U.S. aircraft would make their way to Spain.