カルリスタ戦争
Coinciding with a turbulent period in Basque history (the Carlist Wars, World War I and World War II, the Spanish Civil War, Spain under Franco) bertsos were a popular way of reflecting on current issues and events, like in "Norteko ferrokarrilla", on railway. Although bertsos which were considered to be worthy of passing on had been passed on orally before, the "bertso-paperak", "bertso papers", became popular in this period and are the main source of information on these early bertsos today. They could become an effective means of spreading support for one political position or another during the Carlist Wars, e. g. "Muñagorriren bertsoak".