Final answer:
North Korea declared its own time zone 30 minutes behind South Korea to assert its independence. The Nationalists, after their defeat in the Chinese civil war, fled to Taiwan, and in the Korean War, North Korea invaded South Korea.
Step-by-step explanation:
The country that declared its own time zone, 30 minutes behind South Korea is B) North Korea. This action was part of North Korea's assertion of independence and difference from South Korea. While most countries adopt time zones in whole hours, North Korea chose to establish its time zone that deviates by half an hour.
Answering the additional questions provided, when the Nationalists were defeated in the Chinese civil war, they retreated to A) Taiwan. During the Korean War, B) North Korea invaded South Korea, sparking an international conflict. Lastly, after the Vietnamese conflict, Vietnam was divided between a Communist north and a capitalist south, with Hanoi as the center of the north and Saigon as the center of the south.