By the spring of 1943, American military planners had begun to create a plan to dislodge Japan from east and southeast Asia. To do so, parts of the Philippines were considered main strategic points in the potential Allied attack in the Pacific. The end goal of the Allied plan was an invasion of the Japanese home islands, in which heavy aerial bombardment would precede a ground assault. In order for this to occur, Allied forces would have to occupy areas surrounding Japan, with China adding to Luzon (the largest island in the Philippines) and Formosa (a large island off the coast of China) to create a triangle from which they could launch their bombers.
When Admiral Chester Nimitz was directed to capture an island in the Bonin group, Iwo Jima stood out for its importance in making progress against the mainland, with three airfields that would allow American air forces to attack the Japanese mainland. But the Japanese were also well aware of how important Iwo Jima was, and they fought desperately in bunkers and tunnels that required the Americans to carefully clear them out gradually.
Near the end of 1944, as Allied forces were pushing across the Pacific and edging ever closer to Japan, plans were drawn up to invade the Ryuku islands, the most prominent of them being Okinawa. Given the horrific nature of the combat, and the fact that it was incessant for several weeks, it's no surprise that Okinawa had a profound psychological effect on the men who fought, but it also greatly influenced the thinking of military leaders who were planning subsequent campaigns, including a potential invasion of the Japanese mainland. The casualty tolls at Okinawa ultimately helped compel President Truman to use the atomic bombs on Hiroshima and Nagasaki in an effort to end the war before having to attempt such an invasion.
