Vietnam is a larger (by perimeter, not area), more developed, and more forested country, with a different style of warfare altogether. The United States wasn't ready for guerilla techniques. They expected modern battle tactics and were blindsided by a people who had perfectly used their environment. Venezuela meanwhile is quite different from 1960s Vietnam. Their population is about 16% smaller than 1964 Vietnam, with more urbanization. I.E. less "run through the jungle" and more "run through the favela".