To gain better goods , and also it might be cheaper to buy from china based on the money and u could make more off of it by selling it for more were u live
Too help increase relations and help out each other. If Japan produces more fish than they need they can trade it off somewhere where it would be more valuable. So lets say they send it too America in-trade for fruits, or even oil. with each gaining something the other doesn't they both come off positive.
