Final answer:
In the World System Theory, the poor countries that rely on one type of economic activity for core countries are called peripheral nations. These countries have little industrialization, unstable governments, and are economically dependent on core nations for jobs and aid.
Step-by-step explanation:
In the World System Theory, the poor countries that have economies relying on one type of economic activity, such as extracting and exporting materials for the core countries, are called peripheral nations. These countries have very little industrialization, unstable governments, and are economically dependent on core nations for jobs and aid. They often provide raw materials and agricultural products to the core countries. Examples of peripheral countries include Vietnam and Cuba.