Hiroshima was established on the delta coastline of the Seto Inland Sea in 1589 by powerful warlord Mōri Terumoto, who made it his capital after leaving Kōriyama Castle in Aki Province. Hiroshima Castle was quickly built, and in 1593 Mōri moved in. Terumoto was on the losing side at the Battle of Sekigahara.
During World War II, the Second General Army and Chūgoku Regional Army were headquartered in Hiroshima, and the Army Marine Headquarters was located at Ujina port. The city also had large depots of military supplies, and was a key center for shipping.
On Monday, August 6, 1945, at 8:15 a.m., the nuclear weapon "Little Boy" was dropped on Hiroshima from an American Boeing B-29 Superfortress, the Enola Gay, flown by Colonel Paul Tibbets, directly killing an estimated 70,000 people, including 20,000 Japanese combatants and 2,000 Korean slave laborers. By the end of the year, injury and radiation brought the total number of deaths to 90,000–166,000. The population before the bombing was around 340,000 to 350,000. About 70% of the city's buildings were destroyed, and another 7% severely damaged.
On September 17, 1945, Hiroshima was struck by the Makurazaki Typhoon (Typhoon Ida). Hiroshima Prefecture suffered more than 3,000 deaths and injuries, about half the national total. More than half the bridges in the city were destroyed, along with heavy damage to roads and railroads, further devastating the city.
Hiroshima was rebuilt after the war, with help from the national government through the Hiroshima Peace Memorial City Construction Law passed in 1949. It provided financial assistance for reconstruction, along with land donated that was previously owned by the national government and used for military purposes.
In 1949, a design was selected for the Hiroshima Peace Memorial Park. Hiroshima Prefectural Industrial Promotion Hall, the closest surviving building to the location of the bomb's detonation, was designated the Genbaku Dome (原爆ドーム) or "Atomic Dome", a part of the Hiroshima Peace Memorial Park. The Hiroshima Peace Memorial Museum was opened in 1955 in the Peace Park.
Hiroshima was proclaimed a City of Peace by the Japanese parliament in 1949.