defend themselves from what?
If the US and South Korea were the aggressors, why would North Korea even exist?
North Korea attacked South Korea to spread the vile, hateful, intolerant, genocidal, racist, disease of communism. It exists only b/c when the Chinese resolved to keep their puppet, to perpetuate the slaughter of 60 million human beings and the destruction of untold hundreds of millions of lives ... Truman wet himself and refused to defend the people.
In the interim, numerous opportunities have arisen to take North Korea back. Were we the aggressors, would not the potential for losses would have been irrelevant compared to our overwhelming superiority?