Where did the idea that free markets are "efficient" come from?

I believe in the efficiency of open markets. However, some third-world countries areNEVER going to get out of poverty; this is for a variety of reasons:
-too many people: a nation like Bangladesh simply cannot growfast enought to provide a decnt living for its citizens
-no resources: a land-locked, resource-por country like Chad isn’t ever going to be rich
-tribalism: untill the peoples of the third world abandon tribalism,therewillnever be much economic growth.
However, the assumption that free markets are efficient is simply good information theory…an open market allows producers to know what consumers want, and allows them toadjust their production accordingly. Inthe former USSR, all production decions were made by burocrats-which is whymeeting the target of the “Five Year Plan” was the most important thing, not producing what people wanted to buy!