Final answer:
Major sources of heroin for the U.S. during the late 20th and early 21st centuries were Southwest Asia, Southeast Asia, and Latin America, with significant production coming from Afghanistan and the 'Golden Triangle' as well as from Latin American countries like Colombia and Mexico.
Step-by-step explanation:
The question pertains to the heroin trade and its impact on the United States during a specified, but not mentioned, time frame. During the late 20th and early 21st centuries, the regions that became major sources of supply for heroin in the United States were primarily located in Southwest Asia, Southeast Asia, and Latin America. Southwest Asia, especially Afghanistan, has been identified as one of the world's largest producers of opium, which is the raw ingredient for heroin. In the so-called 'Golden Triangle' of Southeast Asia, encompassing countries like Myanmar and Laos, heroin production also flourished for many years. Additionally, Latin America, with countries like Colombia and Mexico, became significant suppliers, harnessing routes that were originally established for other types of narcotics.