What would happen if North Korea actually launched the nuke?

[Meclazine for Israel]

80-85% chance it would get shot down, every bit of Norks military gear would be destroyed over the next several weeks.  Sadly, a lot of S,Koreans in Seoul would die.  There is a greater than zero chance that the PRC inserts itself on one side or the other.

But they ain't launching sh**t in anger at anybody.  A coup by the military or the PRC as suggested by Ray G is much more likely.

It would be shot mid air.

https://en.m.wikipedia.org/wiki/United_States_national_missile_defense

The USA would have helped South Korea build a defensive wall of missiles designed to intercept such an attack.

Trump has asked South Korea to pay for this wall.

[Meclazine for Israel]

How good are the US's anti missile missiles?

it's a secret

Lol. It's good Torie against states with a few missiles.

ABM - Anti-ballistic missile. Isreal has them, Russia has them but the USA has heaps.

It struggles against a regime like Russia where they will lunch hundreds of dummy missiles.

But against North Korea or Iran, would work a treat.

One of the interesting programs was the Sentinel system:



It was replaced by the Safeguard system in the late 1960's.

The Russians complained about these systems and a treaty was reached in 1972. The Anti-Ballistic Missile Treaty limited the US and Soviet Union to two ABM sites each.

But the USA pulled out:

"On 13 June 2002, the United States withdrew from the Anti-Ballistic Missile Treaty and recommenced developing missile defense systems that would have formerly been prohibited by the bilateral treaty. The action was stated as needed to defend against the possibility of a missile attack conducted by a rogue state."

and so little is known about the expense or characteristics of the 2017 versions of these systems.

As to the question "What would happen if a nuclear weapon is launched from North Korea towards the USA?" then:

https://www.youtube.com/watch?v=i2pB39aYe8E