The domino theory was believed that if one country went communist, the rest of the countries around them would also join them and be communist. In the vietnam war however, the domino theory was the basis of containment for the United States. This containment strategy was to stop communist aggression in South East Asia. I hope this helps!
This excerpt from a letter is a critical primary source, since it was written in the first person and shows the extent to which many patriots during this time were willing to risk their lives for liberty.
