10 Widely Believed U.S. Government Conspiracy Theories

FDR Knew Pearl Harbor Was Going to Happen
Japan landed a devastating attack on Pearl Harbor in 1941. But there's no proof that the U.S. government knew of this in advance. Photo12/UIG via Getty Images

Long before 9/11, the deadly Japanese bomb attacks on Pearl Harbor rocked a nation that had grown accustomed to being left alone, thanks to sheer geography and military capabilities. The U.S. had largely pledged to stay out of the way of Europe's ongoing carnage during World War II. On Dec. 7, 1941, however, the death of 2,400 U.S. troops at Pearl Harbor in Hawaii caused President Franklin D. Roosevelt to band together with the Allied forces to take down Germany, Japan and Italy [source: Goddard]. A serious surge of patriotism and outrage stoked the fire of imminent U.S. involvement, significantly helping FDR's case for war. So, was this changing of the tides due to an unforeseeable, catastrophic attack? Or was it a government manipulation designed to affect public opinion, and thus make it acceptable for the U.S. to take sides?

Declassified documents, publicized in a 2011 book, show that FDR and his cohorts were warned in a memo three days before the attacks that the Japanese were eyeing Hawaii as a target. Conspiracy theorists point to that as ammunition for their claim that the U.S. government knew exactly when the "sneak attack" was going to happen. However, the book's author said the U.S. government "believed the Japanese were contemplating a military action of some sort, but they were kind of in denial because they didn't think anybody would be as audacious to move an army thousands of miles across the Pacific, stop to refuel, then move on to Hawaii to make a strike like this" [source: Bedard].