Though his famous equation (E=mc^2) made the bomb theoretically possible, Einstein had no direct role in the Manhattan Project. When he saw the devastation, he reportedly said, "If only I had known, I would have become a watchmaker." By 1946, with the Cold War brewing, Einstein knew he had to speak out. The result was his stark essay:
The most quoted line from this speech (often misattributed to a letter) is: "The unleashed power of the atom has changed everything save our modes of thinking, and thus we drift toward unparalleled catastrophe." In the 1946 speech, he expanded this: "We think in terms of nations. We fight for flags. But the bomb does not respect the flag. It respects only the map." Though his famous equation (E=mc^2) made the bomb
"The atomic bomb has changed the nature of war. It has made war not merely more destructive, but actually irrational. There is no conceivable defense against it." We fight for flags