No. Japanese was never part of Chinese. Although Japan had given
China centuries of kowtowing and tributaries, and even the king of
Japan would sign off as "Humble subject of China Emperor", the
mainland never had any interest in sinicizing the Japs.
Japan was known as the hermit kingdom for most part of her history.
Although records during Qin Shihuang era suggest tht japanese
people had chinese ancestry.
Think on USA's position, they fought 3 asian wars in the past 50
years, namely korean war, vietnam war, and more recently iraq
war.
USA is a democratic country, the congress and president would need
a lot of support to engage in a war. Would a typical hillbilly
white american support his country to fight a war half the world
around? no..chances are he is more concern about his country's
problems e.g. slowing economy and wealth gap.
If they won, what they gain? if they lost what they gain?
Demographics showed tht Americans themselves detest fighting these
unneccesary wars. (remember hippy period?)Eventually, none of all
these Asian war really aided USA in her interest. Except for WWII
that brought Japan down to her knees.
As for your views on NK, NK only have 1 reluctant friend, which is
PRC. NK is more of a parasite living of PRC's resources. No one in
East asia wants a war that would make Korea stronger.
Instead, things should work the other way around, USA should
applease China so that China would go against NK. With the new
generation of Chinese leaders, relationships with NK and PRC have
already gotten downslide. No one likes NK.
China would receive worldwide damnation if she supported NK. China
isnt a dumb country, though communist too, she knows where she
stands in the world.