Why did the fighting in the Pacific result in so many casualties for the United States

Japanese tradition of death before dishonor meant that there was no surrender for Japanese soldiers, and hence a massive amount of American and Japanese lives were lost, due to Japan clinging to every island they had in the Pacific. On a larger scale this never surrender mentality made the Americans come to the conclusion that they needed a complete and total surrender to be forced on Japan, but also because of the casualties that would likely be taken from a full scale invasion of the Japanese Home Islands, would lead to the idea of simply dropping two Atomic Bombs on some of Japan's most prosperous cities.

answer:

it caused mass african migration, african populations to grow, african empires to topple, and racism against slaves to emerge.