The Japanese and Koreans were not thinking straight when they declared a Nation War. In the end, they had it coming. Instead of toppling another kingdom, they had their own kingdom toppled first. Worst yet, not only have they failed to kill the Steward, their entire fleet of players were completely wiped out as well. Everything that happened was witnessed by the entire world.
Though China may have won both Defensive and Offensive wars, the sudden attack of Japan and Korea was a good wake up call for all the players. To prevent future attacks, they would have to increase their alertness in every Territory. Truth be told, China was lucky. However, they might not be this lucky in the next attack.