Why did the united states drop atomic bombs on the japanese cities of hiroshima and nagasaki in 1945?

To ensure total and unconditional surrender by Imperial Japan

Explanation:

In the final year of World War II, the Allies prepared for an invasion of the Japanese mainland that was sure to incur heavy casualty. This decision was consequently followed by a conventional air strike campaign which destroyed 67 Japanese cities. The war in Europe was officially over when Germany on May 8, 1945 signed its instrument of surrender and the Allies attention was turned to the war in the Pacific.

The Allies immediately asked for the unconditional surrender of the Imperial Japanese armed forces on July 26, 1945, with the option being "prompt and utter destruction".

Japan stubbornly ignored the ultimatum and the war continued.

So the United States according to the Québec agreement agreed with Britain to use atomic bombs on the cities of Hiroshima and Nagasaki.

On August 6, 1945, the first atomic bomb named Little Boy was dropped on Hiroshima.

Three days later, another bomb called Fat Man was dropped on Nagasaki. The effects were devastating as the death toll rose to about 250,000 across the two cities in the first to four months.

Japan unequivocally surrendered subsequently

The launching of atomic bombs on Hiroshima and Nagasaki was the form used by the United States to force Japanese surrender in the context of World War II. The purpose of this act was to force Japan to surrender and prevent a likely invasion of that country, which would result in thousands of allied soldiers killed.