The United States of America bombed Hiroshima and Nahasaki with the Atomic Bomb. Hiroshima was bombed first on August 6 1945 with the nuclear weapon nicknamed "Little Boy", and the atomic bomb "Fat Man" on Nahasaki on August 9 1945. It is debateble wheather these bombings were ethical or not.
Actually, Hiroshima is in Japan, but yes, it was bombed by America. The two Japanese cities of Hiroshima and Nagasaki were bombed by American atomic bombs, the only two ever used in war (so far). The bombing terrified Japan, and this led the Japanese to stop fighting in World War II.