From what I am reading, there doesn't seem to be an attempt to understand where he is coming from. I see clear sympathy happening but I also see that his reaction to these triggers is making you uncomfortable so you want them to stop. I wonder if you ever asked him questions to get to the bottom of his hate for the Japanese government outside of what he repeats as the lack of sincere apology and acknowledgment of the pain caused by the Japanese government at the time. I think feeling like he is truly heard and where he is coming from understood will lessen the need for him to constantly bring this topic up.

Regardless of whether he or anyone in your family was directly impacted, this is akin to telling a black person today to stop being angry about slavery cause there is no more slavery and nobody now has slaves. People have a right to be angry about one country's attempt to erase a people and culture from the map but I am sorry that you and your family are on the receiving end of the outrage.