Final answer:
The quote by President Eisenhower refers to the issue of the domino theory in the 1950s. This theory suggested that communism in one country would lead to other neighboring countries also becoming communist, like a row of dominos falling. The quote influenced US policy in Southeast Asia, as the US aimed to prevent the spread of communism and support non-communist governments.
Step-by-step explanation:
The quotation by President Eisenhower is referring to the issue of the domino theory in the 1950s.
The domino theory was the belief that if one country in Southeast Asia fell to communism, then neighboring countries would also fall like a row of dominos. The quote highlights the concern that if one country became communist, it would lead to a chain reaction of other countries also becoming communist.
This belief influenced US policy in Southeast Asia, particularly in Vietnam, as the US sought to prevent the spread of communism and support non-communist governments in the region.