They thought: if we are going to get our share of the new world order, we have to act as aggressively and as forcefully as the Germans, in the Pacific.
They believe the war would be short and a new arrangement would be diplomatically reached, which acknowledged their superiority and sphere of influence. They believed they needed the raw materials and markets of the Pacific under their control, in order to survive and thrive.
All of it made a sort of sense. It simply turned out, most of their assumptions were wrong.