Some additional considerations here: (1) climate change is probably not going to be good for the global agriculture market and (2) the nearest country with lots of farmable land is China, a country Japan has not historically gotten along with.
China and Japan actually only hated each other in the last 100 years (maybe 50). If you look at the period of time of last 2000 years China and Japan were on much more reasonable terms.
Zhou Enlai said,“two thousand years of friendship and five decades of misfortune,” about the relationship between China and Japan.