This is why Asian Americans are on the bottom of the totem pole. Instead of fighting against anti-Asian racism it is always Japanese Americans against Korean Americans, Taiwanese Americans against Mainland Chinese Americans, or even worse when it is Chinese on Chinese. How could you expect others to respect you when you don't even respect yourself?
East Asia today is more like Europe in the early 20th century - ie hardly an unified region. Europe isn't even unified today, as seen by the extreme hostility between Russia and its allies, and the West and its allies. Think about how much the Poles hate the Russians; then compare that to China, Korea, and Japan. The Poles are even a Slavic people, highly related to Russians.
So it isn't particularly surprising to see conflict between East Asians. The Americans are an exception in this regard - they're all about the "white race" because that's the only unifying force in America, since the European immigrants in the US aren't unified by any other identity, they needed the concept of the "white race" to hold them together.
Old World Europeans, by contrast, were never that enthusiastic about the "white race." The Germans looked down on the Slavs as an inferior race and wanted to enslave them. European racial scientists made a distinction between the various sub-races of Europe and politicians thought of them in zero-sum terms - ie Nordic interests must come at the expense of those other "sub-races" of Europe who should be enslaved or driven off to make space. That was the underlying current through much of World War 1 and 2.
In other words, East Asians hating each other is actually pretty "natural" if you want to compare to other Old World cultures and civilizations.
What's out of the ordinary is the hegemonic "white" identity that the US has been able to create post-World War 2 through its domination of Europe (outside of Russia) and North America.