The failure to have Spain join the Axis
German forces fought in support of Francisco Franco during the Spanish Civil War, as did the Italians, and Franco himself was a Fascist dictator. Yet despite numerous diplomatic overtures and negotiations including Spain gaining North African possessions, Franco could not be persuaded to join the Axis militarily. In political positions, the Spanish dictator was close to Mussolini, but the Italian leader was equally unsuccessful in persuading Spain to support the Germans and Italians. Spain relied on imports from the United States for most of its oil, and Franco may have been reticent to go to war so soon after the Spanish Civil War, which had been long and costly.
In fact, though politically aligned with the Nazis and Fascists, Spain became a haven for escaping Allied prisoners of war and Jews fleeing the Nazis. Spain also became a hotbed of spies and espionage agents from all of the combatant nations through their embassies, consulates, and business activities there. Hitler finally grew to be disgusted with Franco, and refused to have any further contact with him as the deteriorating situation in North Africa and then the Mediterranean made Spain a less important strategic position. Had Spain been persuaded to join the Axis it would have opened additional Atlantic ports to the U-Boats, as well as making the British base at Gibraltar untenable.