Not quite sure what the question totally is but I have two answers
The bloody fighting on these islands made America hesitant to invade Japans home island because the casualties would be severe.
If the question is asking why we wanted the Islands, it was to secure them to build airfields where we could launch bombers and be in range of Tokyo.
Hope this helps.
Answer:
It made the U.S president Truman believe that force was necessary to stop Japan aka the bombing of Hiroshima.
