Wozza said:
This is a bit ASB.
why would North Vietnam not invade South Vietnam?
Well, there are a couple of reasons. First, if the US hadn't decided to screw around with the French or Diem, there wouldn't be a division of the country. Hence no war.
Second, at least according to Sheenan (Bright Shining Lie), Ho and company actually were busy in the late 50s with the "socialism in one country" model. Collectivization had come close to shattering the North, so they weren't looking for trouble. The earlier analogue is Stalin seeking to maintain the peace of Europe in order to have time to purge the society. Communist Terror doesn't go well with a major international war.
Meanwhile in the South, the Viet Mihn (Viet Cong was mainly an American term) were facing such pressure from Diem's campaign against them that they felt they had to strike. Once the southern campaign began, Ho and Giap felt that they had to support their comrades or risk losing control.
If the southerners hadn't been as threatened or if Diem had managed to push them harder (and hadn't screwed over the rest of the population in the process), the North might not have intervened and focused on problems closer to home.