The NYT publishes an extensive review of string theory

The New York Times > Science > String Theory, at 20, Explains It All (or Not)

The string revolution had its roots in a quixotic effort in the 1970's to understand the so-called 'strong' force that binds quarks into particles like protons and neutrons. Why were individual quarks never seen in nature? Perhaps because they were on the ends of strings, said physicists, following up on work by Dr. Gabriele Veneziano of CERN, the European research consortium.

That would explain why you cannot have a single quark - you cannot have a string with only one end. Strings seduced many physicists with their mathematical elegance, but they had some problems, like requiring 26 dimensions and a plethora of mysterious particles that did not seem to have anything to do with quarks or the strong force.

When accelerator experiments supported an alternative theory of quark behavior known as quantum chromodynamics, most physicists consigned strings to the dustbin of history.

---

A very thorough summary! Despite reading some popular books on the topic, I'd not known that string theory's first iteration was back in the 1970s, nor that Feynman had done it in with QCD.