After extensive research, Japan claimed Senkaku in 1895 right before Sino-Japane war. China only got interested after UN disclose potential for oil in 1970s.
Senkaku is NOT contested any more than mainland china can be contested by Zhou decedent living in Japan. Some native american can claim ownership of USA, but USA is not contested land.
Right map shows Senkaku is twice closer to Japan(Ishigaki islands) than mainland china and about same distance to taiwan.
Left 1969 Chinese map Senkaku(尖閣) proving china believed it was part of Japan.
USA violated geneva/hague convention and ILLEGALLY interfered with Japanese constitution which even German was NOT victim of. Literally, even police was not allowed to carry a weapon. Also allies were made immune from prosecution and koreans were added probably to used as a henchmen. Rampant crimes occurred as well as S korea invaded Takeshima island and killed few dozen fishermen. Because of this and Korean war/cold war interpretation became slightly loose and police were allowed to carry weapon as well as self defense force was allowed.
After WW2, USA refused Korean request/lies and USA returned Takeshima island to Japan. S Korea invaded Japan and killed few dozen fishermen to take Takeshima.
S korea continue to illegally occupy japanese island. They Japan bash in hope to turn world opinion in hopes of manipulating outcome in international court. 1957 Korean text book claim Takeshima is not Korean.
Kuriru shima 北方四島
First modern boarder was set in 1855 with these 4 tiny island as Japan. Currently, only valid boarder was from settlement of Russian-Japanese naval war of 1905. Russia committed geneva/hague convention war crimes by killing civilian, rape, stealing civilian land, attacking surrendering troops, forced labor, etc. So international law wise, Russia must return half of Sakhalin and other tiny Japanese islands. I think Japan should wait for Russia to go broke or lose WW3 and get all back.
Google “real7777 guningtoun battle” to find out how japanese nemoto saved ROC/Taiwan from fake oppressive communist. It also contain how he defeated coward russian that attacked civilians,raped women, and attacked unarmed solders that were surrendering to US.