What were America's motives in dropping the atomic bomb in Hiroshima?

America sought to save the lives of potentially millions of its soldiers by causing Japan to surrender before it had to be invaded.

Explanation:

As America came closer to the Japanese homeland at the end of World War II, battles with the Japanese prior suggested that the Japanese would cause over one million combat deaths along with other casualties. Since they were already militarizing their population, had years to entrench themselves for any invasion, and put strategic targets in urban areas to discourage bomb raids; it was decided to nuke 'em.