Dear FastNed,
I do not have the particular book for an exact quote(it is at work) but "in 1986, Liberia was subjected to a military coup wherein almost the entire gov't leadership was liquidated, and a tyrannical dictatorship imposed. This dictatorship was supported by the US as it had large investments there."
source: The World Human Rights Guide, 1987 by Charles Humana
As to the other countries, especially Burma (Myanmar??) drugs are a major source of income for the country, a major source of disposable income back in the US.
Afghaistan and Pakistan, and most of the 'Golden Triangle' have had their share of 'military advisors' and CIA make friends with the warlords at some point.
For Burma, read "The Politics of Heroin" (I don't remember the author, I got it from the library)and for Afghanistan read "Soldiers Of God: The Mujahadeen in Afghanistan" by Robert Kaplan.