Barack Obama will be the first U.S. president to visit Hiroshima. Hiroshima is the first city where an atomic bomb fell. Around 140,000 people died. Some people say it helped end World War II. Mr Obama will not say sorry for the bombing. He will look to the future of the USA and Japan.
Mr Obama said his visit is a time to remember that war is bad. It causes death. It is also to remember the dead. He doesn't want nuclear weapons to be used again. He said innocent people in wars suffer a lot. He added: "And that's not just the thing of the past. That is happening today in many parts of the world."