They flew over South Korean airspace on military exercises, I think the Clear aggression tactics were North Korea threatening to nuke the USA.
In fairness tho, the NK threats are about as serious as me threatening to kill Bono, by summoning Pikachu to give him cancer in his sleep.
Which is why no one is going to do anything about it, apart from saying "tut tut" and carrying on with sanctions. And I'm not even sure that sanctions are doing much good. Doesn't help relations, and looks like they'll get whatever tech they want from Iran anyway.
Apart from sanctions on trading weapons with NK, they should probably scrap the rest of them. (the people of) NK really needs a lot of help.