Is this the prelude to WW3?
No unlikely.
If North korea and South korea would go in a war today, nobody would jump towards the help of North Korea.
Plus, South korea is wel capable of fending off North korea. South korea has modern tanks and a modern airforce.
North korea has maybe 3300 tanks, but S korea has 1500 modern one's up to date, with 900 brand new tanks incoming ( K1A1 and currently the most modern tank of the world= K2 Black panther)
If both would clash again, it would result probaly in an artillery duel maybe. In wich wich artillery can kill wich faster will be the key factor. South korean artillery is more mobile, but North korean has more and more powerfull artillery
Then again, south korea has the US on their side.