Which conflict occurred between North and South Korea to prevent the spread of communism?

The conflict that occurred between North and South Korea to prevent the spread of communism is the Korean War. This war lasted from 1950 to 1953 and was primarily fueled by the tensions of the Cold War, as it involved the North, which was supported by communist allies like the Soviet Union and China, and the South, which was backed by the United Nations, particularly the United States.

The Korean War is significant as it represented an early instance of the United States' strategy of containment, which aimed to stop the spread of communism in Asia and other regions. The tensions that arose after World War II, with Korea divided at the 38th parallel, set the stage for this military conflict. The war ended in an armistice, but no formal peace treaty was signed, and the Korean Peninsula remains divided to this day.

The other conflicts mentioned, such as the Vietnam War and the Cold War, while related to the broader context of communism and its spread, did not specifically involve the same direct military engagement between North and South that characterized the Korean War. World War III is a hypothetical scenario that has not occurred, and thus is not applicable in this context.