Geography played, in one way or another, the dominant role in Japan's desire to expand its empire.
First of all, Japan is a country that lacks natural resources of the sort needed to run an industrial economy. This is a geographic fact. Because Japan lacked such resources, it wanted an empire from which it could obtain them.
Second, geographic luck caused there to be many areas not far from Japan that did have resources. These were places like China, the Philippines, and Indonesia. In this way, geography gave Japan a convenient set of targets to try to take.
Finally, geography placed Japan and its desired empire far from any strong countries. This made it more feasible for Japan to try to take an empire from others in its neighborhood.
In all of these ways, geography helped push Japan to take an empire from others during this time.