Espionage
In World War 2 Espionage was used by the Axis power's (mainly Germany) to uncover confidential information about the Allies plans during the war. The Germans had used espionage to get ahold of economic, military, and political information of the United States before Pearl Harbor had even occurred, till long after the war. On the other hand the United States did use it to obtain information about the axis powers that have not seen the light of day since the end of the war.