The 3 countries historically never like each other and this orange man single-handedly reunited them with a common cause!
In short term they cooperate on tariffs, because America has gone crazy.
On the long term. South Korea and Japan will seek their to ensure their security against China without the US. South Korea is already discussing domestic nuclear weapons. Japan could go nuclear at any time when it wants.
On some level, Trump clearly understands that this sort of cooperation would be a problem for him (https://www.politico.eu/article/trump-threatens-eu-and-canad...), but I'm not sure if he understands that it is _inevitable_.
> If American policy is what keeps them apart, which I strongly doubt
No, it's not that. Current US policy is _driving them together_, however.
The best case scenario for USA is we are able to hold on to secure elections, Democrats move towards something like Ezra Kleins’ vision and MAGA collapses and a more values based party takes their place.
I'm not saying that this isn't a possible economic alliance, but it's an unlikely one, and the evidence provided for it isn't really up to the task.