Labor Day wasn’t always about hot dogs and corn hole.
In fact, the holiday stemmed from a series of violent actions against workers in the late 19th century who were protesting miserable working conditions in an era where laborers were afforded few rights or protections. The hard fought struggles, which ultimately resulted in a marked improvement in labor conditions in many U.S. industries and helped spur an era of strong labor unions and expanded workers rights, is an essential part of American history but far too commonly overlooked.
These short videos provide a good overview on the history of Labor Day. Additionally, these articles from PBS and Scientific American give good background information, as does this Lowdown post on May Day and its relation to Labor Day.