Comparing Iraq/Afghanistan is like comparing chalk and cheese...the countries themselves were never a direct threat the western nations.
North Korea as a state however has openly admitted to wanting to destroy the US and South Korea, and while it may just be bluster is anyone willing to test that. As Trump has said, NK should have been dealt with years ago when they were 'less' of a threat and potentially an 'easier' conflict to win. Prolonging the regimes survival just buys them more time to strengthen their military and weapons at which point any preemptive attack would be disastrous.
While I'm not condoning a conflict which could cost hundreds and thousands of lives, action now could save future lives.
Or... or... maybe they'll get their nukes and feel slightly more secure, and not attack anyone.
Your talk of "lets attack them first!" is precisely the reason they feel so insecure.
We talk about preventing war, but who do you want to start a war right now? Us - the West. Is it any wonder countries feel threatened when the West has started two world wars, are the only ones to use nukes, and are the ones itching to start more wars? In the name of "peace"?
Let's face it... attacking them would already have catastrophic consequences. Realistically, all we can do is de-escalate. If that's even possible with Trump in charge.