Argentina
Buenos Aires, which was by then the capital of the Viceroyalty of the Río de la Plata, was attacked during the British invasions of the Río de la Plata. As the regular military forces were not enough against the British armies, Santiago de Liniers drafted all the male population capable to bear arms into the military. This included the criollo peoples, who were down in the social hierarchy, and even slaves. With these reinforcements, the British armies were defeated twice.
The militias became a strong factor in the politics of the city afterwards, as a venue where the criollos could manifest their political ambitions. They were a key element in the success of the May Revolution, which deposed the Spanish viceroy and began the Argentine War of Independence. A decree by Mariano Moreno derogated the system of promotions by castas, allowing instead the promotions by military merits.
The Argentine Civil War was waged by militias again, as both Federals and Unitarians drafted common people into their ranks for the ongoing conflicts. This type of warfare began to decline by the 1870s. It was definitely outlawed by Julio Argentino Roca, who established the conscription.
Read more about this topic: Militia