The United States under orders of President Truman.
Manhattan
During WWII, It was dropped in Hiroshima.
A- bomb stands for Atomic Bomb, first tested and used in WWII.
WWII
The first atomic bomb was engineered in WWII, not the Cold War. The Hydrogen Bomb was a Cold War Weapon.
During his work on the atomic bomb during WWII, he and his group at Fermi Labs discovered numerous new elements.
'Little Boy' was the code name for the atomic bomb that was dropped on Hiroshima during World War II. This is the first atomic bomb that was ever utilized as a weapon.
When Japan bombed Pearl Harbor that was a reason for the USA to enter WWII. It then led to the atomic bomb.
It ended WWII.
Japan, to end WWII.
It ended WWII & the world entered the "Atomic Age."
== == It was an effort to convince Japan to surrender during WWII