 After expanding the war in the Pacific to include Western outposts , the Japanese Empire had attained its initial strategic goals quickly , taking the Philippines , Malaya , Singapore , and the Dutch East Indies ( now Indonesia ) ; the latter , with its vital oil resources , was particularly important to Japan . Because of this , preliminary planning for a second phase of operations commenced as early as January 1942 . There were strategic disagreements between the Imperial Army ( IJA ) and Imperial Navy ( IJN ) , and infighting between the Navy 's GHQ and Admiral Isoroku Yamamoto 's Combined Fleet , and a follow @-@ up strategy was not formed until April 1942 . Admiral Yamamoto finally succeeded in winning the bureaucratic struggle with a thinly veiled threat to resign , after which his plan for the Central Pacific was adopted . 
