Jeri mentioned the Ludlow Massacre thread. The one about 1913 Massacre - Historical Background also deserves attention.

In some cases threads like this have actually unearthed and preservew memories and history that might have otherwise got forgotten. Other times the information they contain might be available to scholars or historians already, but they provide it in a way that makes it available to the people singing the songs, and ensures that there are people singing them with understanding of where they come from, and what they are about.