Final answer:
Frank and Wallerstein's theory categorizes countries into core, semi-peripheral, and peripheral nations, which helps in understanding global economic stratification and the various challenges each type of nation faces.
Step-by-step explanation:
Frank and Wallerstein developed a theory that distinguishes between core nations, semi-peripheral nations, and peripheral nations.
Core nations are considered highly developed or industrialized, which includes countries like the United States and Japan. Semi-peripheral nations are often referred to as developing or newly industrialized, such as Brazil and India. Peripheral nations are relatively undeveloped and include many countries in regions such as sub-Saharan Africa and parts of Asia.
This differentiation is important in understanding global stratification as well as the specific challenges and issues faced by countries at different levels of development, particularly in sectors such as healthcare, political stability, and economic growth.