The Domino theory was proven right after Vietnam when similar uprisings and wars happened in Cambodia Laos Thailand and Malaysia.
Step-by-step explanation:
Cambodia Laos Thailand and Malaysia are neighboring nations to the state of Vietnam that saw one of the most gruesome wars of its time.
This is followed by similar militias forming in these batons too and some erupting into a full blown war by the sponsoring of the two great superpowers
of the time.
This was good evidence for the fact that it in fact is true that one event in one place can cause a similar event in another neighboring place.
This was the essential doctrine of the Domino theory.