Why does u.s.a "librate" oppressed pplz in iraq but not in china or north korea ? If its that humanistic ?

I hear lots of crap here 4m deluded americans abt how they liberated pplz in iraq and how its a "democracy" nw ! Okay i ll agree 4 a second . . . Why dont u guys liberate other oppressed pplz in NK OR china . . . Or they have to be in a weak country - near to israel - having lots of oil ? If u ll say that iraq threaten u.s.a (somehow) nk , china are more of a threat !