Why did the US Naval Fleet make Pearl Harbor a permanent home for the pacific fleet?

According to a site, it says to discourage japanese agression in the pacific.

what agression? what were they doing?
What was japan's agression in the pacific during the 1940s

The Japanese were expanding into asia and threatining to expand into the pacific. When relationships between the US and Japan began to break down in the late 1030's the US moved its fleet to a position were it could react faster to any Japanese aggression agaisnt US held territoy.