Explanation

The United States developed the first atomic bomb.

During World War II under the Manhattan Project.

Which was dropped on the Japanese cities of Hiroshima and Nagasaki.

The Little Boy type of bomb was dropped on the Japanese city of Hiroshima on 6 August 1945.

The Fat Man was dropped on Nagasaki, Japan, on August 9, 1945

Hiroshima deaths: around 40000 

Nagasaki deaths: around 80000

Additional information:

Germany is the first country where first controlled fission of an atom was carried