The Island of iwo jima
The island of Iwo Jima acted as a base for intercepting the American Bombers and sending a message to the homeland that there were incoming planes. The American bombers could no longer fly over the Japanese islands without being detected by Iwo Jima. In order to counter the Japanese base's interception the American bombers would dog-leg around the island adding to the already lengthy travel. However, the Japanese were still able to detect the planes. In order to launch an attack on the homeland, America would need to get rid of Iwo Jima.