The key issues the United States based fighting Japan across the Pacific ocean

Japanese reluctance to surrender would prove a major challenge for the United States in the Pacific Theater. It meant every rock in the water the US gained would be gained with tremendous amounts of American and Japanese bloodshed alike. Ultimately not wanting to go through the trouble of invading the entirety of the Japanese Home Islands would be the reasoning behind dropping the Atomic Bombs on Hiroshima and Nagasaki, rather than fight for years and years and leave millions more dead. Other than that in the opening phases of the war following the Japanese attack on Pearl Harbor the US Pacific Fleet was heavily damaged, and while ultimately the US Pacific fleet would get back on its feet, it gave Japan an early advantage allowing them to invade the Philippines and the Dutch East Indies.