Excerpts from Books and Wikipedia
"The liberation of Latin America in the 1820s had proceeded with such speed that many border issues remained unresolved until later in the century. One such problem was Bolivia's access to the sea through the Atacama Desert between Chile and Peru, a region rich in guano, a major source of the valuable nitrates used in saltpeter and fertilizer production. Bolivia's demand for taxation and seizure of the Chilean Antofagasta Nitrate and Railway Company in February 1879, brought military retaliation by the Chilean army. Peru, which had signed a secret alliance with Bolivia in 1873, was drawn into the dispute, forcing Chile to declare war on both countries.… The war continued for several years as Peru resisted--with tacit US assistance--until a peace treaty was signed in 1883. According to the treaty's terms both Bolivia and Peru had to cede mineral-rich territory to Chili, and the provinces of Tacna and Arica were to vote in 10 years on their nationality. Peru and Bolivia had suffered hugely, both physically and economically, from the war, and tensions between the combatant countries still exist." [Furtado: 1001 Days]