[I]t was the Yankees and not Korean “reds” – a tiny force even in their 1920s heyday — whom the Japanese authorities were most intent on infamizing. … - Brian Reynolds Myers

The North wants unification under its own flag, while South Korean progressives want the two states to coalesce over decades of mutually beneficial economic cooperation.

Since Moon's takeover the peninsula has become less like divided Germany than ever. The ROK has abandoned the competition for legitimacy, instead ceding the North’s superiority on nationalist grounds while reaffirming that these matter more than liberal democratic ones. I’m not sure a league will ever come about, but if it does, it will hitch a proudly radical nationalist state to an unloved, moderate-nationalist one too shamefaced to celebrate its own founding. If the South is already unwilling to criticize the North, or to renew a commitment to its own constitutional values, it’s hardly likely to mount a strong defense of human rights later on.

If anything, the North Koreans are probably going to be more inclined to behave themselves in the run up to the election in May. They do not want to do anything that would help a conservative candidate and a North Korean nuclear test would force either Moon or Ahn or both those candidates to make some kind of hard-line statement which they could of course back on and probably would go back but it would at least delay the resumption of unilateral aid to North Korea and Kim Jong-un quite possibly want that.