Opium. Afghanistan is the largest opium producer in the world (source in comments).
Wars are generally about economics. They are about money. Things never change. People think that is all in the past, but that is not the case. Did you know the Vietnam War was also about opium and the raw resources of Southeast Asia?
Check these primary source documents:
Here are a couple of passages from the Pentagon Papers that refer to the opium trade:
Page 4 of this document discusses the "French controlled monopolies on salt, alcohol, and opium..." The next page (5) discusses Binh Xuyen, the gang that evolved from the Black Flag pirates. The CIA agent, Edward Lansdale, cited how the gang's leader, Le Van Bay Vien, colluded with the French and Bao Dai to control gambling and prostitution. He ran an opium factory and ran a distribution system. (Source in comments from [Part V. B. 2. a.] Justification of the War. Internal Documents. The Truman Administration. Volume I: 1945 - 1949 )
Another is a Truman administration document discussing Vietnam. There is a section discussing foreign trade, part of which reads: "The central government has derived its chief income from custom fees, excise taxes and monopolies, of which the opium monopoly is the most lucrative." (source in comments, page 185)
Some of this stuff is right in the open, but people don't seem to notice or care. The sentiment of the remarks made by Eisenhower are often really downplayed today, just like in the past. Wars often have several causes, but I always start with the economics. Many people downplay the economics or ignore it altogether.
Excerpts from President Eisenhower's Remarks at Governors' Conference, August 4, 1953, Public Papers of the Presidents, 1953, p. 540:
"Now let us assume that we lose Indochina. If Indochina goes, several things happen right away. The Malayan peninsula, the last little bit of the end hanging on down there, would be scarcely defensible--and tin and tungsten that we so greatly value from that area would cease coming...., because finally if we lost all that, how would the free world hold the rich empire of Indonesia?........."So, when the United States votes $400 million to help that war, we are not voting for a giveaway program. We are voting for the cheapest way that we can to prevent the occurrence of something that would be of the most terrible significance for the United States of America--our security, our power and ability to get certain things we need from the riches of the Indonesian territory, and from southeast Asia."