Before any further discussion, here is the Wikipedia page on the dispute:

https://en.m.wikipedia.org/wiki/Senkaku_Islands_dispute

China and Taiwan posit their claims mainly because of their proximity to the islands, and some historical records. Japan stipulates their claims from its late 19th century survey and the islands’ status of terra nullius at the time.

I claim no neutrality to this issue: I’m a US citizen of Chinese descent, and this issue is a sticking point in Sino-Japanese relations and one of the very few things that both Chinas agree and cooperate.

At the end of the day, we are all but humans, and these are just artificial lines and names on the map, but I do think it is important to look a bit more into the claims before further discussions.