However, death and destruction per se do not mean democracy cannot grow, both Germany and Japan went through terrible loss of life and infrastructure before becoming model democracies.
Yes, but they are hardly comparable to Vietnam.
Germany had existing parliamentary system and tradition, even if the Weimar Republic was hardly stabile and probably not even what we call democracy nowadays. It was also totally impossible for (West) Germany to lapse back to totalitarianism because it was heavily occupied.
Japan on the other hand indeed developed democracy. However, it was also industrialised like Germany and didn't have the similar colonial legacy as Vietnam had. I must point out also, that I have always considered the Japanese democracy a bit odd case, if you think that the local conservative party has been ruling the country since the end of occupation 1951 and not until now the opposition is developing to be a real opposition. I believe that has very much to do with cultural differences between the Japanese and the West. After all, not even their view to capitalism is quite the same.
Vietnam on the other hand had colonial past of a century and no existing examples of such requirements for democracy as established journalism etc.
It is interesting to note that communists were so popular in (South) Vietnam, because the population consisted mainly out of impoverished peasantry. In the same time, North Vietnam was redistributing land and thus dismantling the old colonial system, something that really appealed to South Vietnamese landless or substenance farmers. On the other hand, under Diem government there was no way such redistribution would happen. I think this is what ties Vietnam much closer to Indonesia than Taiwan or Korea - affecting much more than western interests for resources - the appeal of communism to the landless peasants and that communism had to be suppressed violently.