And tomorrow is the 71st anniversary of the atomic bombing of Hiroshima. The bombing killed 140,000 people and seriously injured another 100,000. Three days later, the U.S. dropped a second atomic bomb on Nagasaki, killing another 74,000 people. In May, President Barack Obama became the first sitting U.S. president to visit Hiroshima. He spoke at a memorial for victims of the attack, but disappointed some by failing to offer a formal apology for the bombing. The U.S. is the only country ever to have dropped an atomic bomb.