I believe the USSR and Japan have not yet signed a peace treaty. The USSR declared war on Japan a couple of days after the bombing of Hiroshima. They immediately invaded Manchuria and turned over Japanese weapons to their buddy Mao. They thought their three-week war effort entitled them to half of Japan. After four years of war, we weren’t ready to give it to them. But thanks to their war-time sacrifice we ended up with Red China and North Korea. They still have some islands that Japan considers Japanese.
After we agreed to the armistice in Korea in 1953, Red China turned over many of the captured US weapons to the Viet Minh; the French were furious that we’d made that deal that ended up costing them dearly (while they fought a war they hadn’t even wanted; we convinced them to fight it).
There’s no USSR now, so it would be like signing a treaty with the Holy Roman Empire. I see Russia & Japan are dancing around to come to some sort of a treaty. Probably to try and get the Kuril Islands back. Can’t see Russia doing that, lot of military investment has been made there.
Great if they did.