The outcome of the Pacific war was directly related to the ability of the Americans to adjust strategy to the realities of the Pacific war, a unity of effort directed by the National Command Authority and superior industrial, technological and logistical capabilities. The Japanese after initial success did little to adapt and were hamstrung by inter-service rivalries and inadequate industrial capacity and limited natural resources.
The Japanese and the Americans each had war plans in place for the Pacific campaign. The American plans, Plan Orange had been developed since the early part of the 20th Century after the Spanish-American War and Russo-Japanese War. Predicated on holding the Philippines until relief could arrive Orange assumed that the US Pacific Fleet would sail across the Pacific and fight the Japanese Navy in a manner written about by Alfred Thayer Mahan; see Weigley in The American Way of War and Ronald Spector in “Eagle Against the Sun: The American War Against Japan.”
IJN Carrier Hiryu heavily damaged and abandoned at Midway. Hiryu, Akagi, Kaga and Soryu the creme of the Japanese carrier fleet were lost at Midway, the Japanese found it hard to replace them or their decimated air crews
The Japanese were conflicted. The Navy desired a campaign that would destroy the American Navy and expand the Empire to the East and to Southeast Asia and the Indian Ocean. The Army was fixated on the China strategy having been embroiled on the Asian continent since the early 1930s. John Toland discusses this in good detail in his book “Rising Sun: The Decline and Fall of the Japanese Empire 1936-1945” In addition other Japanese Army leaders had designs on Siberia and fought a brief campaign against the Soviets which ended in a defeat.
When the Japanese attacked Pearl Harbor as well as the Philippines and Southeast Asia defeating American and Allied forces in detail, crippling the American Navy and dooming the Philippines the Americans were able to adjust strategy to first a defensive one supplemented by raids against the Japanese perimeter by carrier forces and the beginnings of a nascent submarine campaign against Japanese merchant shipping. The Americans were able to parry the Japanese thrust at the Coral Sea and inflict a major defeat on the Japanese Carrier Forces at Midway prior to launching the first limited offensive by the Navy and the Marines at Guadalcanal.
The Japanese remained mired in their conflicting strategies with the Navy primarily fighting the Pacific campaign aided by limited Army and Army Air Forces on the islands Japan had occupied or fortified while the bulk of the Army was engaged in China, Southeast Asia or sitting on the Manchurian-Soviet border.
Once the Americans shifted to the offensive a campaign of island hopping coordinated between the Southwest Pacific Area under General MacArthur and the Central Pacific Area under Admiral Nimitz focused on gaining control of islands which contained airbases and anchorages capable of sustaining the American advance while bypassing islands not necessary for this along with their Army garrisons. Both American advances in the South Pacific and Central Pacific focused on retaking the Philippines and cutting the Japanese lines of communication and supply with Southeast Asia. From late 1942 on the Japanese strategy was focused on individual areas of danger versus a overall coordinated defensive effort.
The Japanese were hamstrung from the beginning of the war by limited natural resources, especially oil and oil refining capacities, limited industrial capacity, especially in the realm of the manufacture of steel and machining tools. All of these were supplied in large part by their opponents and were cut off once the war began.
Michael Barnhart in his book Japan Prepares for Total War” has an excellent account of the limitations of Japanese economic, industrial and natural resource capacities, as well as the continual struggle by the Army and the Navy for priority in access to them and the inability of Japanese planners, both civilian and military to resolve this conflict. The Americans had a different situation; although American industrial capacity was enormous it had to be split between to Theaters of Operations and support the needs of American Allies, Britain, the Soviet Union, Canada and China.
Despite this the Americans in a relatively short time were able to amass forces equal to or great than the Japanese who were unable to replace losses in ships, aircraft or the highly trained personnel needed to man them. At the beginning of the war Japanese Air and Naval forces in the Pacific outmatched everything the Allies could offer, however once they began to experience significant losses at Midway and during the Guadalcanal Campaign their air and naval capabilities diminished to the point that they had to conserve ships and aircraft hoping to be able to gain local advantage in critical defensive areas.
New American ships and aircraft introduced during the war were superior to Japanese designs, many of which had reached their apex by 1942. American advantages in radar, communications equipment added to American advantages throughout the war. Japanese ground forces in the Pacific were dependant on the Navy and merchant marine for supply and reinforcements. As the American submarine campaign became better organized this became more difficult as the American submarines copying German Wolf pack tactics decimated the Japanese merchant Marine. I particularly like Samuel Elliott Morrison’s account of this in “The Two Ocean War” and “The History of US Navy Operations in World War II” which has a volume devoted to this subject.
Japanese forces would always fight determined battles but they often expended great amounts of manpower in senseless Banzai charges rather than make the Americans force them out of well prepared positions. Where the Japanese maintained excellent defense such as at Tarawa and Iwo Jima they made the Americans pay greatly for their gains. American Marines were apart from the 82nd and 101st Airborne Divisions were the best infantry in the US Military and their skill at amphibious operations and integrated air-ground and naval warfare increased as the war went on. The Americans were well equipped with modern weapons while the Japanese operated antiquated tanks and often substandard artillery.
Japanese leadership at the strategic and political level was inept throughout the war. They failed to coordinate any strategy with the Germans and failed to enunciate any sort of Grand Strategy. On the operational and tactical levels the Japanese forces, especially the surface navy performed well, however as the American numeric and technologic advantage increased the Navy became less effective. After the death of Admiral Yamamoto in 1943 Japanese Naval Leadership became far less effective. The Americans as mentioned before were able to devise a Grand Strategy which not only dealt with Japan but also Germany and coordinated the efforts of forces, war production, planning and logistics to advance their war aims. At the operational and tactical level American forces, especially the Navy and Marines and later the Army Air Forces and Army became more skilled and than their Japanese counterparts with the possible exception of General Simon Bolívar Buckner at Okinawa. See Spector and Thomas Costello “The Pacific War.” In the air the Americans continued to increase their combat capabilities at the tactical and strategic level and used massed fire bombing raids to devastate the Japanese homeland. The Japanese in contrast due to inexperienced pilots and fewer competitive aircraft were forced into suicide or Kamikaze missions as the war neared Japan.
The outcome of the Pacific war was directly related to the ability of the Americans to adjust strategy to the realities of the Pacific war as well as the unity of effort which enabled the American superiority in industrial, technological and logistical capabilities to overwhelm the Japanese. The Japanese after initial success did little to adapt and were hamstrung by inter-service rivalries and inadequate industrial capacity and limited natural resources, fell behind in technology and were unable to replace losses among the ships, men and aircraft that they needed to fight an effective war. Japanese leaders at many levels failed to adapt strategy, tactics or methods to match the reality of the war and the places that they did do so were done by local commanders and never instituted throughout the Japanese military.