i'm not overestimating the US. i'm just saying that there are, at least, a divisions worth of soldiers solely from the US in seoul. this is, of course, disregarding the fact that there is an entire south korean army, the third army, stationed in and around seoul and the western DMZ. not counting their airforce, which will scramble just as quickly as the USAF.
but okay, if you think north korea can scooby doo 50,000 soldiers, trucks, tanks, etc past all of this without anyone noticing.
and all of this is on wikipedia.