The Fifth Column: During the Spanish Civil War (1936-1939), Nationalist General Emilio Mola referred to his subversives in Madrid as the "fifth column" of his army corps. That is, Mola saw the people who clandestinely worked to undermine the Second Spanish Republic as the ultimate factor in his pursuit of victory. When the four primary columns of the Nationalist army approached Madrid, Mola asserted that the fifth column had already taken control of the city through underground efforts. Nevertheless, the Siege of Madrid lasted over two years, so the effectiveness of Mola's fifth column is certainly debatable. For the most part, the Spanish Civil War can be viewed as a dress rehearsal for World War II insofar as Fascist Italy and Nazi Germany gave substantial aid to the Nationalists while the Soviet Union provided arms to the Republicans. In a way, the Spanish Civil War represented the first battleground of World War II. And yet, little did Europeans know, the Second World War would be many times more deadly and destructive than the First - due in large part to advances in warfare technologies like the airplane, tank, and submarine.