America would go in and start another war (as it did the first time, and has done with most countries in the Middle East); Japan would assist America where it could, but would leave them to most of the work; China would either partially support the North or just stay out of the conflict.
Probably if North Korea started a war, USA would go on and help South Korea for they are more friendly and because of similar government. China would help North Korea because of their similar government too. Japan would help South Korea because they are more of a close friend. Not because of a similar government. ---- if North Korea started a war, it would be my guess that USA, Japan, and China will help South Korea because North Korea is trying to send nuclear bombs to USA and other places.
it's china -________________-
The neighboring countries of North Korea are South Korea, China, Russia, Japan, and Mongolia.
Japan fought against China and Korea.
Korea
China and North Korea have poorer economy compare to South Korea and Japan.
Japan is by China, the coasts of North Korea and South Korea and next to the sea of Japan.
Japan has no bordering countries since it is made of islands. The five closest countries to Japan are (in order) Russia, South Korea, North Korea, China, and Taiwan. North and South Korea, Russia and China.
The four countries closest to Japan are China, Russia, North Korea, and South Korea.
The Neighbors Of Japan Are RUSSIA AND CHINA
Japan, China, South Korea, North Korea, Vietnam, Laos.
Diffusion from Korea and China