This 1985 stamp of Brazil commemorates the sesquicentennial of the Farroupilha Revolution, or Ragamuffin War (1835-45) of that country. The painting of mounted secessionists was done by Brazilian modern realist Guido Mondin.
The uprising was caused by economic conditions. The state of Rio Grande do Sul, in the south, relied on internal trade, whereas the rest of the country was mainly dependent on exports of raw materials. The war came only 10 years after Brazil's independence.
From Wikipedia, "It is considered the longest and third bloodiest of the failed wars of secession in the Brazilian Empire." There were 20,000 deaths from this uprising. This is quite a large number of casualties considering there were 20,000 national soldiers fighting 14,000 rebel troops.