During the second half of the 19th century the Atacama Desert became the world's most important nitrate / saltpeter producing region, much of it to satisfy a huge world demand for fertilizers. Hundreds of Oficinas Salitreras / Saltpeter Works and towns for the workers were constructed in the so called Nitrate Pampa in the Regions of Tarapacá (then part of Peru) and Antofagasta (most of which was then the Litoral Province of Bolivia). After the War of the Pacific (1879 to 1884) between Chile and a Bolivian Peruvian alliance the region became part of Chile. The War is also known as the Nitrate War, as disputes between Bolivia and Chile over nitrate taxation and concessions for Chilean nitrate companies operating in Bolivian territory were the main causes. The increasing production of synthetic nitrates and fertilizers after World War I led to decline in the industry and by the mid 20th century most of the Oficinas had shut down. Many of these abandoned former mining sites can still be visited; 2 of the best known, the Humberstone and Santa Laura Saltpeter Works near Iquique, were declared a UNESCO World Heritage Site in 2005.