Why was the u. s. afraid to drop the bombs on japan in wwii? what would happen after they attack them that would not be good on their part?

Because America was there 2nd goal the entire eastern side of the world was what they wanted to conquer first so if they dropped the bomb and japan sent there entire force at America say bye bye murica

While the United States began conventional bombing of Japan as early as 1942, the mission did not begin in earnest until mid-1944. Between April 1944 and August, 1945, an estimated 333,000 Japanese people were killed and 473,000 more wounded in air raids. A single firebombing attack on Tokyo in March 1945 killed more than 80,000 people. Truman later remarked, “Despite their heavy losses at Okinawa and the firebombing of Tokyo, the Japanese refused to surrender. The saturation bombing of Japan took much fiercer tolls and wrought far and away more havoc than the atomic bomb. Far and away. The firebombing of Tokyo was one of the most terrible things that ever happened, and they didn't surrender after that although Tokyo was almost completely destroyed.”

In August 1945, it was clear that conventional bombing was not effective.

I hope this helps