B. It brought about the unconditional surrender of Japan.
Not A, the bombs were dropped instead of invading, which had a very high estimated casualty rate if the US did.
Not C, Germany eventually faltered and caved in, and then surrendered in the European Theater.
Not D, the Japanese Empire was using Kamikaze attacks longs before Atomic weapons were developed.
Intergrated but uneqaul
After slave labour, americans found itself with a problem of intergrating blacks into the system, but the main headaches after 1920's was the question of equality, that led to emergence of rigorous activism.
No, it is not true that the development of armies, navies, and weapons is called imperialism. This would be called "nationalism". Imperialism refers to when countries take over and dominate other countries.