In Japan and South Korea there is deepening concern over the reliability of long-time American security guarantees – whether the U.S. will come to their aid in the event of a war. This has been turbo-charged by Donald Trump’s tough treatment of traditional U.S. allies, which has some in Tokyo and Seoul calling for a reassessment of their non-nuclear policies.
There’s still alot of animosity from South Korea towards Japan. The threat from China and American unreliability has driven them together politically but the animosity still remains on an individual level.