Vietnam interfere in Laos for some reaons, Khmers problem is just a excuse. You just check the map of Vietnam, they have no strategic depth from West to East, they need to expand its strategic depth by devouring Laos. China will never allow them doing it. Vietnam leaders seduced by Soviet and it's aspiration had lost control in 1970s, they all blame it on CHina.
The history of this region is filled with constant warfare for the control of the region; the Siamese, the Burmese, the Vietnamese all were vying for dominance in this region. Too small of a region and too many factions involved with an appetite for conquest. Cambodia and Laos are unfortunate because their population is too small and thus they are a small shrimp between two large whales (Thailand and Vietnam).
As for Vietnam. They prefer to keep Cambodia and Laos militarily weak so as to exert their influence on them. I mean, afterall, what better way to control your satrap than to keep them extremely weak to resist your power.
In regards to Vietnam-China relations; it would have been better for them both (China and Vietnam) had the CPV aligned itself with the CPC. In fact the strategic depth of the Sino-Vietnamese sphere could have been realized all the way up to Thailand.
But again, this is all 20 - 20 perspective.
@Nihonjin1051 How do you perceive Abe's goverment?
1. I like his policy of greater Japanese military responsibilities
2. I do agree with him that immigration quota needs to be amended and Japan should remove its excessively strict immigration / protectionist policy
3. I agree with his policy of courting Russian cooperation and signing a formal peace treaty with Russia and solve the border issue in the north
4. I disagree with him visiting Yasukuni Shrine during socially sensitive moments
5. I believe that he should have made a formal apology to China and Korea about WWII
6. I do not agree with his lack of action regarding the TPP and the CJK-FTA.
I like some of hi policies, and I do not approve some of his policies.