If Japan was already in the 2nd Sino-Japanese War, why would they attack Pearl Harbor?

I just learned about the 1st and 2nd Sino Japanese Wars, the 2nd of which started 4 and a half years before pearl harbor. I know Japan was busy with that, and the occupation of Korea. Just learning this as an adult, it makes it even more confusing why on earth Japan would attack the U.S. Can anybody make a reasonable justification from the 1940s Japanese governments point of view how that would make any sense strategically? What was there to gain in any way?