How can 130million people live on 4 islands, where no Resources and earthquake and volanco happen nearly everyday? Since China was very weak in the history, holding a huge area without a suitable Power? Why not Japan invaded China? Japan did try to attack USSR and USA, while result, as we all know. So do you remember what I said? Having fine weapon is not to attack others, but to keep the war away from you.Most Mongols have now became an ethnic group in China, they are proud of the Chinese identity, so we forget about the past.
We can also forgive Japan, but Japan yet still doesn't give up the dream of conquering China, Thus, we can't become friend with them.
BTW, we didn't invade Vietnam nor we wants their land, the 1979 war was a border conflict.
But Japan always wants our land.